A    HANDBOOK    OF    TESTING 

MATERIALS 


A   HANDBOOK  OF  TESTING 


C.  A.  M.  SMITH,  M.  Sc.  (ENG.), 

A.M.I.  MECH.  E.,  A.M.I.E.E.,  LATE  K.N.,  ASST.  PROFESSOR,  EAST  LONDON  COLLEGE 
(UNIVERSITY  OF  LONDON)  ;  AUTHOR  OF  "  SUCTION  GAS  PLANTS." 


MATERIALS 


NEW    YORK 

D.    VAN    NOSTRAND    COMPANY 

23,    MURRAY,    AND    27,   WARREN    STREETS 

191 1 


PREFACE 

All  technical  colleges,  and  many  of  the  large  engineering 
works,  now  possess  a  laboratory  furnished  with  apparatus  for 
the  testing  of  materials.  It  is  hoped  that  some  portion  of  this 
book  may  be  of  service  to  engineers  engaged  in  practice ;  it  is, 
however,  written  primarily  for  the  college  student,  although  a 
great  engineer  has  said  that  one  of  the  attractions  of  our  work 
is  that  we  are  always  students  in  engineering.  If,  at  times* 
the  reader  thinks  that  the  descriptions  of  apparatus,  or  of  tests, 
are  somewhat  detailed,  he  should  remember  that,  although  he 
may  be  quite  familiar  with  a  machine  or  process,  other  readers, 
possibly,  have  not  had  the  same  opportunities. 

The  chief  object  of  the  author  has  been  to  interest  engineers 
in  experimental  work.  The  experience  gained  in  four 
colleges,  and  a  works  testing  department,  has  led  to  the 
belief  that  the  great  importance  of  experimental  work  is  not 
sufficiently  recognised.  It  is  hoped  that  students  may  be 
stimulated  to  look  up,  both  before  and  after  they  have  made 
experiments,  the  description  of  the  apparatus  and  tests  men- 
tioned. The  diagrams  will  perhaps  be  useful  for  sketching 
purposes. 

The  methods  of  teaching  engineering  vary  in  the  different 
centres.  No  attempt  is  made  in  this  book 'to  standardise  such 
methods — each  instructor  is  the  best  judge  of  what  suits  the 
plant  and  the  students.  A  list  of  experiments  is  given  in 
Chapter  XIL,  as  it  may  be  useful  to  those  who  are  commencing 
to  organise  a  laboratory  course. 

The  illustrations  have  been  made  especially  for  the  book. 
Attention  has  been  given  to  the  scheming,  as  well  as  the 
actual  drawing  and  reproduction  of  diagrams,  in  the  hope 
that  the  details  of  the  apparatus  described  may  be  made 
clear.  An  effort  has  been  made  to  avoid  catalogue  illus- 
trations. In  some  places — especially  in  the  chapter  on 


372 J SO 


vi  PREFACE 

alternating  stress  machines — the  diagrams  used  in  the  Pro- 
ceedings of  Societies  and  technical  papers  have  been  replaced  by 
others  drawn  with  the  object  of  showing  principles  rather  than 
details  of  construction.  In  the  Appendices  there  are  included 
discussions  on  certain  researches,  which  have  been  included 
for  the  advanced  student.  Some  of  these  researches  are  so 
recent  that  they  have  not  been  previously  described  in  a  text- 
book on  materials.  Further  experiments  may  be  suggested  to 
the  reader  by  a  study  of  the  methods  used  and  results  obtained. 

The  number  of  instructors  in  college  laboratories  are 
frequently  insufficient  for  their  arduous  duties.  It  is  sug- 
gested that  the  book  will  assist  the  instructors  and  students 
by  reason  of  the  various  experiments,  methods,  and  data 
recorded.  It  is  advisable  to  take  a  group  of  not  more  than 
ten  students  and  explain  the  apparatus  to  be  used  to  them. 
It  is  usually  inconvenient  to  take  notes  during  such  demon- 
strations, and  the  contents  of  the  book  may  therefore  be  useful 
to  the  student  for  reference  purposes.  During  the  conduct  of 
the  ordinary  laboratory  work  the  most  suitable  number  to  be 
engaged  on  one  experiment  is  (usually)  three.  Suggestions  are 
given  in  the  Introduction  concerning  the  record  of  such  work. 

The  author  begs  to  thank  numerous  friends  who  have  dis- 
cussed the  contents  of  the  book  for  their  assistance.  His 
assistant,  Mr.  V.  C.  Davies,  B.Sc.,  has  not  only  carefully  read 
through  the  proofs,  but  made  many  useful  suggestions  con- 
cerning the  contents  of  the  book.  Mr.  E.  J.  Surman,  B.Sc., 
has  also  helped  to  revise  the  proofs.  It  is  therefore  hoped 
that  the  book  is  free  from  misprints,  etc.,  but  the  author 
would  be  glad  to  hear  of  any  that  are  noticed  by  readers. 
The  following  have  kindly  granted  permission  for  the  extracts 
from  their  publications,  viz. :  editors  of  technical  journals 
mentioned,  British  Engineering  Standards  Committee,  Institu- 
tion of  Civil  Engineers,  Institution  of  Mechanical  Engineers, 
Physical  Society,  etc. 

C.  A.  M.  S. 

LONDOX, 

June,  1910. 


CONTENTS 


CHAP.  PACiE 

I.    INTRODUCTION   . „  1 

II.  GENERAL   PROPERTIES   OF   MATERIALS 7 

III.  MACHINES   FOR   TENSION,  COMPRESSION,  AND   BENDING   TESTS  .  16 

IV.  STRAIN-MEASURING   INSTRUMENTS 51 

V.   METHODS   AND   RESULTS   OF   TESTS   ON   MATERIALS   ...  83 

VI.   TORSION   TESTING 116 

VII.   IMPACT  AND   HARDNESS   TESTS 137 

VIII.    SHEAR   AND   MISCELLANEOUS   TESTS 155 

IX.   ALTERNATING   STRESS   TESTS •        .  168 

X.   THE     TESTING     OF     CEMENTS,      REINFORCED      CONCRETE,     AND 

STONES 189 

XI.    THE   TESTING   OF   TIMBER.  .  .  .  .  .  .  ,207. 

XII.   EXPERIMENTS   IN   COLLEGE   LABORATORIES         .  .  .  .213 

APPENDIX   I.    STANDARD  RESULTS  OF  TESTS  ON  THE  STRENGTH 

OF   MATERIALS 227 

„          II.    ADMIRALTY     RULES    FOR     TESTING     MATERIALS 

FOR   MACHINERY 234 

,,         III.    RESEARCHES   ON   COMBINED    STRESS     .            .            .  236 

IV.    HEAT   TREATMENT    OF    STEELS     ....  260 

BIBLIOGRAPHY 265 

USEFUL   CONSTANTS 270 

INDEX                                                                                                                               .  277 


LIST    OF    ILLUSTRATIONS 


PIG.  PAGE 

Testing  Machine  for  Testing  up  to  300  Tons  in  the  University 

of  Birmingham     .         ...  .         .         Frontispiece 

1.  Curves  showing  Effect  of  varying  Percentages  of  Carbon  in 

Steel  on  the  Tenacity,  Hardness  and  Ductility  of  the  Material       1 1 

2.  Diagrammatic  Sketch  of  Vertical  Type  Testing  Machine  .         .       18 

3.  Diagrammatic  Sketch  of  Horizontal  Type  Testing  Machine      .       19 

4.  Wicksteed's  Testing  Machine    .  .         .         .         .20 

5.  Sir  Alexander  Kennedy's  Testing  Machine        .         .         .         .22 

6.  Diagrammatic  Outline  showing  Principle  of  Werder  Machine  .       24 

7.  Side   Elevation  of  300-ton  Testing  Machine  in  Birmingham 

University     .         .         .         .         .         .         .         ...       25 

8.  End  View  of  300-ton  Birmingham  Testing  Machine         ,f        .       26 

9.  Details  of  Poise   Gear  and  Levers  on  Birmingham  300 -ton 

Machine         .         .         .         .         .         .         ,         .         .         .27 

10.  Details  of  Main  Earn  on  Birmingham  300-ton  Machine    .         .       29 

11.  Amsler  Testing  Machine  for  Short  Compression  Specimens       .       35 

12.  Riehle  Testing  Machine 37 

13.  General  Arrangement  for  Girder  Testing .         .         .        :..        .       38 

14.  Apparatus  for  Testing  Deflections  of  Beams      .         .         .         .       40 

15.  Change   Speed  Mechanism  in  Poise  Gear  of  Riehle  Testing 

Machine        .         .         .         .         •         •         ...         .       42 

16.  Details  of  Knife-Edges,  Shackle,  and  Grip         .  .       45 

17.  Ball  Seating  for  Tension  Specimens  with  Screwed  Ends    .         .       46 

18.  Ball  Seating  for  Specimen  in  Compression         .  .       47 

19.  Method  of  Loading  Compression  Specimen        .         .         .         .       48 

20.  Unsuccessful  Method  of  Loading  Compression  Specimen          .       48 

21.  Prof.  Lilley's  Method  of  Testing  Hollow  Struts         ...       48 

22.  Diagram  showing  Effect  of  Wear  of  Knife-Edge  in  Machines 

of  the  Wicksteed  Type  .  .       49 

23.  Ewing's  Extensometer      ...  .  .52 

24.  Diagrammatic  Outline  of  Latest  Type  Ewing's  Extensometer  .       53 

25.  Unwin's  Extensometer      ......  .55 

26.  Marten's  Pointer  Extensometer         .  .       56 

27.  Ashcroft's  Extensometer  ...  .56 

28.  Kennedy's  Extensometer  .  •       57 

29.  Stromeyer's  Rolling  Pin  Extensometer     .  .       58 

30.  Stromeyer's   Rolling  Pin  Type    Extensometer    (as  used  on 

finished  structures) 59 


x  LIST  OF  ILLUSTRATIONS 

FIG.  PAGE 

31.  Cambridge  Extensometer 60 

32.  Bauschinger's  Mirror  Extensometer           .....  61 

33.  Marten's  Mirror  Extensometer 62 

34.  Detail  of  Mirror  Attachment,  Marten's  Extensometer       .         .  63 

35.  Stromeyer's  Optical  Extensometer     ......  64 

36.  Strips  for  Sphingometer 65 

37.  Section  through  Sphingometer  Strip  Holder      ....  66 

38.  Strip  Carrier  and  Specimen  Grip  for  Sphingometer  ...  67 

39.  Calibration  Curve  for  Sphingometer  Strip          ....  69 

40.  The  Sphingometer,  fitted  with  Torsion  and  Tension  Strips       .  70 

41.  Un win's  Stress-Strain  Recorder 73 

42.  Wicksteed's  Stress-Strain  Recorder   ......  74 

43.  Hemiing's  Portable  Autographic  Stress-Strain  Recorder .         .  76 

44.  Kennedy's  Automatic  Stress-Strain  Recorder  ....  78 

45.  Autographic  Stress-Strain  Recorder  as  attached  to   a   Single 

Lever  Machine       .........  79 

46.  Autographic  Diagram  taken  with  Apparatus  shown  in  Fig.  45  80 

47.  Autographic  Stress-Strain  Recorder  with  Double  Pencil  Gear 

giving  Two  Scales  for  the  Extension 81 

48.  Standard  Tension  Specimen  Plate 83 

49.  Typical  Tension  Specimen  Bar  ...  .  .83 

50.  Screwed  End  for  Tension  or  Compression  Specimen  ...  84 

51.  Ultimate  Tension  Test  on  Muntz  Metal     .....  86 

52.  Tension  Test  on  Aluminium      .         .         .         .         .         .         .86 

53.  Distribution  of  Extension           .......  89 

54.  Typical  Compression  Specimen  .                  .                   ...  90 

55.  Short  Ductile  Specimen  in  Compression    .                  ...  90 

56.  Ball  and  Socket  Joint        ...                           ...  90 

57.  Real  and  Apparent  Stress-Strain  Curves  in  Compression  (from 

single  observations)        ........  92 

58.  Appearance  of  Ductile  Compression.     Specimen  at  Failure       .  93 

59.  Shear  Stress  on  Brittle  Material  in  Compression       .  93 

60.  Fracture  of  Ductile  Material  in  Tension 94 

61.  Fracture  of  Cast-Iron  in  Compression 94 

62.  Resolution  of  Forces  in  a  Specimen  subjected  to  Tension          .  95 

63.  Mild  Steel  Plates  in  Tension  (Autographic  Diagram)         .         .100 

64.  Curves  of  Real  and  Apparent  Stress          .         .         .         .         .101 

65.  Autographic  Diagram  of  Mild  Steel  in  Tension,  showing  Effect 

of  removing  temporary 102 

66.  Effect  of  Time  and  Low  Heat  Treatment  on  Mild  Steel  in  Tension  103 

67.  Effect  of  Time  and  Boiling  on  Mild  Steel  Specimen  in  Com- 

pression         .         .         .         .         .         .          .         .         .         .104 

68.  Curves  showing  Effect  of  Heat  Treatment  on  Bessemer  Steel  105 

69.  Curves  showing  Mechanical  Hysteresis      .....  106 

70.  Mild  Steel  in  Tension  108 


LIST  OF  ILLUSTEATIONS  xi 

FIG.  PAGE 

71.  Sphingometer  Test  on  Muntz  Metal         .         .         .         .         .113 

72.  Cast -Iron  under  Torsion  .         .         .         .         .         .  .116 

73.  Fracture  of  Cast-Iron  Hollow  Specimen  in  Torsion          .         .     117 

74.  Torsion  Test  on  Mild  Steel  (Autographic  Diagram)  .     118 

75.  Stresses  induced  in  a  Bar  subjected  to  Pure  Torsion         .         .     119 

76.  Bailey  Torsion  Testing  Machine       .         .         .         .         .         .     120 

77.  Hand-Torsion  Testing  Machine        .  .     123 

78.  Diagram  of  Torsion  Meter       .         .         .         .         .  .124 

79.  Effect  of  Overstrain  in  Torsion  (Mild  Steel  Specimen)    .          .125 

80.  Effect  of  Overstrain  on  Mild  Steel  in  Torsion  .     ^    .  .     126 

81.  Effect  of  Time  and  Boiling  on  Mild  Steel        ....     126 

82.  Effect  of  Overstrain  and  Boiling  on  Mild  Steel  in  Torsion       .     ]  27 

83.  Effect  of  Overstrain  and  Boiling  on  Mild  Steel  in  Torsion       .     127 

84.  Pure  Torsion  Test  on  Aluminium  showing  Time  Effect  .         .128 

85.  Torsion  Tests  on  Aluminium    .         .         .         ...'..         .     129 

86.  Torsion  Tests  on  Copper  .         .  .                   .         ...     129 

87.  Effect  of  Overstrain  on  Copper        .         .         .       ...         .         .     130 

88.'  Torsion  Tests  on  Muntz  Metal                    .                  .         .         .     130 

89.  Torsion  Tests  on  Muntz  Metal          .         .         .         .       '.bi        .     131 

90.  Eectangular  Block  under  Shear  Stress     .         •       j  •         •         .132 

91.  Circular  Specimen  in  Torsion  .        ,.    ;     .         .    '     .         '.'       .     132 

92.  Apparatus  for  Torsion  Experiments  on  Wires .      ;  .        >        .     134 

93.  Apparatus  for  Testing  Torsional  Vibrations  of  Wires       .         .136 

94.  Impact  Testing  Machine •'.  .         .         .139 

95.  Impact  Testing  Machine,  repeated  Hammer  Blows          ..        .     143 

96.  Unwhrs  Apparatus  for  Hardness  Tests    .         .  -       ...         .     145 

97.  Brinell's  Machine ..'.-.         .148 

98.  Apparatus  for  Shearing  Tests  .         .  .         ...         .156 

99.  Apparatus  for  Punching  Tests          .         .         .         f         .         .     158 

100.  Punching  Test  op  Mild  Steel   .         .         .         .         ...     159 

101.  Apparatus  used  for  Testing  Steel  Balls    .         .         .         .         .     161 

102.  Steel  Ball  Tests .162 

103.  Small  Beam  Testing  Machine  for  Cast-iron     .         .         .         .164 

104.  Work  done  in  Breaking  Specimen 166 

105.  Load-Extension  Curves  showing  Effect  of  Annealing  on  Mild 

Steel 167 

106.  Wohler's  Alternating  Torsion  Testing  Machine        .         .         .169 

107.  Mechanism  of  Wohler's  Tension  Alternating  Stress  Machine  .     171 

108.  Wohler's  Variable  Bending  Stress  Machine     .         .         .         .172 

109.  Wohler's  Machine  for  Eepeat  Bending  in  opposite  directions  .     173 

110.  Diagram  showing  Nature  and  Stress-Cycle  of    the  Wohler 

Test 175 

111.  Diagram  showing  Nature  and  Stress-Strain  Lines  in  Arnold's 

Test 175 

112.  Diagram  of  J.  H.  Smith's  Alternating  Stress  Machine   .         .179 


xii  LIST  OF  ILLUSTRATIONS 

PTG.  PAGE 

113.  Diagram  of  J.  H.  Smith's  Alternating  Stress  Machine    .         .     180 

114.  J.  H.  Smith's  Alternating  Stress  Machine       .         .         .         .181 

115.  Curve  for  Eationalisation  of  Alternating  Stress  Experiments     183 

116.  Sankey's  Hand  Bending  Machine    .         .         .         .  .185 

117.  Autographic  Diagram  from  Hand  Bending  Machine        .         .     186 

118.  Dimensions  of  Standard  Briquette  (British  Standard  Specifi- 

cation)   ....  .  .     190 

119.  Setting  Needle  for  Cement   (British  Engineering  Standards 

Committee's  suggestion)         .        .         .         .         .         .         .191 

120.  Le  Chatellier  Soundness  Testing  Instrument  (British  Standard 

Specification)          .         .         .         .     -  .         .         .  .  .     192 

121.  Cement  Testing  Machine          .     '    .         .  ••      .    '     .  .  .193 

122.  Machine  for  Compression  Tests  of  Stones  and  Cements  .  .194 

123.  Tests  on  Cement  with  Brinell's  Ball  Test         .?       .  .  .     200 

124.  Amsler-Laffon  Beam  Testing  Machine   .         ...  .  .204 

125.  Section  of  Specimen  under  Compound  Stress  .        J  •     236 

126.  W.  Scoble's  Method  of  deciding  Yield  Point    .  .     242 

127.  Distribution  of    Stress  in  Specimen  subjected  to  Non- Axial 

Loading 244 

128.  Arrangement   of  Loading   for   Combined   Compression    and 

Torsion  Experiments     .         .         .         .         .         .         .         .     245 

129.  General  View  of  Combined  Tension  and  Torsion  Apparatus, 

showing  the  Specimen  with  Torsion  Bars  and  Pulleys .         .     246 

130.  Curve   showing  Method  of  Plotting  Results  of  Compound 

Stress  Experiments        ........     250 

131.  Diagram  to  show  Method  of  Loading  in  a  Combined  Bending 

and  Torsion  Test  on  Dr.  Coker's  Apparatus  ....     254 

132.  Professor    Coker's    Apparatus    for   Combined   Bending   and 

Torsion  .    '     .         .         .        '.         .         .         .         . "      . .,  '  ....     256 

133.  Curve  of  Correction  Factor  for  Professor  Coker's  Combined 

Bending  and  Torsion  Machine       .         .         .         .         .         .257 

134.  Professor  Coker's   Torsiometer   for   Measuring   Strains  in  a 

Combined  Bending  and  Torsion  Test 258 


PLATE. 

I.  Fracture  of  Specimen  tested  as  Cast. — Micrographs  of  Cast 
Steel  before  and  after  annealing.  Magnified  28*5  dia- 
meters.— Specimen  tested  when  annealed  (no  fracture) 

To  face  p.       10 

II.     Fractures   of   Wrought-Iron  and   Mild   Steel  in  Tension. — 
Fractures  of  Cast-Iron  in  Compression. — Fracture  of  Cast- 
iron  Specimens  in  Pure  Torsion  .         .         .  To  face  p.       87 
III.     Fracture  of  Various  Materials  in  Tension         .         .  To  face  p.       87 
IV.     Fracture   of  Cast-Iron  Specimens  in  Combined  Torsion  and 

Bending To  face  p.     251 


A    HANDBOOK 


OF 


TESTING     MATERIALS 


CHAPTEK  I 

INTRODUCTION 

Theory  and  Practice.  —  It  is  possible  to  learn  a  great  deal 
of  the  science  which  underlies  all  engineering  work  by  making 
tests  and  experiments.  There  is  a  continuous  use,  and  adjust- 
ment to  correct  perspective,  of  results  obtained  by  theory  and 
practice.  The  work  of  testing  materials  is  very  largely  of 
a  practical  nature.  For  commercial  routine  tests  little  is 
required  beyond  a  knowledge  of  arithmetic  and  a  skill  in  the 
manipulation  of  certain  machines  and  measuring  appliances. 
An  engineering  training  is  necessary  if  the  correct  deductions 
are  to  be  made  from  the  test.  It  must,  however,  be  under- 
stood that  commercial  figures,  although  of  great  value  to 
engineers,  are  not  always  the  only  results  to  be  sought  in 
making  tests,  and  in  commercial  work  it  frequently  happens 
that  new  tests  and  apparatus  must  be  devised. 

The  properties  of  the  materials  used  in  structures  and 
machines  are  of  great  importance.  A  knowledge  of  these 
properties  can  be  best  obtained  by  conducting  a  series  of 
experiments  upon  specimens  or  samples  of  the  various 
materials.  In  making  these  tests,  the  difference  between 
work  done  in  an  engineering  and  a  physics  laboratory  will 
at  once  become  apparent.  Although  there  is  a  certain 

T.M.  B 


2  A  HANDBOOK  OF  TESTING  MATERIALS 

similarity  between  the  methods  employed,  yet  there  will  be 
noticed  in  the  materials  used  and  tested  by  engineers  a 
variation  in  the  properties  of  different  samples  of  the  same 
material.  The  object,  therefore,  of  the  experiments  made 
upon  steel,  iron,  copper,  alloys,  etc.,  is  to  find  average  values, 
rather  than  rigidly  exact  numerical  results. 

The  properties  of  materials  used  by  engineers  vary  owing 
to  many  causes.  If  we  take  a  pound  of  almost  any  gas 
and  measure  its  temperature,  pressure,  and  volume,  we  can 
estimate  with  accuracy  the  behaviour  of  the  gas,  if  it  is  to 
be  compressed,  under  certain  conditions,  to  a  new  pressure 
and  volume.  If,  however,  we  take  a  pound  of  steel  we  cannot 
forecast  with  any  accuracy  the  behaviour  of  the  material 
under  load  if  we  know  nothing  more  about  it  than  the  fact 
that  it  is  called  steel.  It  is  of  some  assistance  if  we  know 
the  chemical  composition  of  the  steel,  but,  even  with  such 
information,  we  cannot  estimate  with  accuracy  the  load  which 
the  material  will  carry  at  the  point  of  fracture. 

Experience  has  taught  engineers  that  the  only  satisfactory 
method  of  estimating  suitable  loads  in  design  works  is  to 
subject  samples  of  the  actual  material  to  be  used,  to  tests, 
which  reproduce,  as  nearly  as  is  possible,  the  conditions  met 
with  in  actual  practice.  Thus,  if  a  quantity  of  steel  is  made 
for  a  purpose  in  which  the  material  is  subjected  to  a  direct 
pull,  the  most  satisfactory  way  of  deciding  the  maximum 
value  of  the  pull  to  be  allowed  in  practice  is  to  test  samples 
of  the  material  under  similar  conditions,  and  obtain  a  record 
of  the  physical  properties  of  these  samples.  Of  course  it  is 
possible  that  all  of  the  steel  from  which  the  samples  have 
been  selected  will  not  behave  in  a  similar  fashion  to  the 
specimens  tested.  In  general,  however,  we  can  obtain  suffi- 
cient data  to  assist  us  to  estimate  with  considerable  certainty 
the  safe  loads  to  which  the  materials  may  be  subjected. 

In  building  a  bridge,  roof  or  other  structure,  or  machine, 
there  are  two  possible  errors  which  may  be  made  owing  to  a 
lack  of  knowledge  of  the  materials  employed.  Insufficient 
material  may  be  used,  in  which  case  there  will  probably  be  a 


INTRODUCTION  3 

collapse.  Too  much  material  may  be  used,  in  which  case 
the  structure  or  machine  will  cost  more  than  is  necessary. 
Although  generally  it  is  not  so  obvious,  yet  the  fault  of  the 
engineer  who  uses  more  material  than  is  necessary  is  as  great 
as  that  of  the  engineer  who  uses  too  little.  All  safe  structures 
and  machines  use  more  material  than  is  theoretically  neces- 
sary, because  a  certain  factor  of  safety,  arrived  at  from  the 
result  of  experience,  is  employed.  The  safe  load  must  not, 
however,  be  reckoned  too  high  or  too  low.  The  most  satis- 
factory method  of  estimating  the  safe  load  is  to  test  one  or 
more  specimens  of  the  material  to  be  used.  From  a  com- 
mercial point  of  view  that  is  the  purpose  of  the  science  of  the 
testing  of  materials.  There  are,  however,  other  reasons  why 
this  work  should  be  undertaken.  These  are  outlined  below. 

The  Testing  of  Materials  Laboratory. — Instruction  in  the 
properties  of  materials  is  given  in  the  laboratory  for  the 
following  definite  objects :  (1)  To  demonstrate  the  behaviour 
of  various  materials  under  stress.  (2)  To  establish  clear  con- 
ceptions as  to  the  meaning  of  fundamental  terms  of  the 
engineer's  vocabulary,  such  as,  yield-point,  ultimate  strength, 
modulus  of  elasticity,  and  shear  modulus.  (3)  To  make  the 
student  familiar  with  the  methods  by  which  materials  are 
tested  to  obtain  such  numerical  results  as  will  enable  their 
properties  to  be  recorded  and  compared  with  other  materials. 
(4)  To  fix  in  the  memory  a  few  average  results  for  the 
materials  more  commonly  used  in  engineering  work.  (5)  To 
lay  the  foundation  for  a  certain  habit  of  thought,  invaluable  to 
the  engineer.  This  might  be  called  cultivating  the  habit  of 
testing  laws  and  materials  (wherever  it  is  possible  to  do  so) 
instead  of  accepting  them  from  authorities.  (6)  To  give  the 
student  practice  in  writing  reports  of  work  done  by  himself. 
(7)  To  undertake  original  investigations  (for  publication) 
calculated  to  advance  the  knowledge  of  the  strength  and 
elasticity  of  materials. 

The  laboratory  experiments,  as  a  means  of  illustration,  must 
go  hand-in-hand  with  theoretical  instruction.  The  latter  will 
place  before  the  student  underlying  principles.  It  will  assist 

B  2 


4  A  HANDBOOK  OF  TESTING  MATERIALS 

him  to  understand,  in  their  correct  perspective,  the  maze  of 
experimental  facts  which  he  will  obtain  during  his  own 
personal  investigations.  It  will  aid  in  developing  habits  of 
clear  and  discerning  thought. 

It  frequently  happens  that  students  are  eager  and  willing 
to  conduct  tests,  but  put  off  the  working  out  of  the  results. 
No  greater  fallacy  exists  than  that  the  test  is  completed  and 
everything  known  when  the  actual  experiment  is  finished. 
Numerical  results  should,  whenever  it  is  convenient  to  do  so, 
be  calculated  in  the  laboratory.  The  slide-rule  is  sufficiently 
accurate.  In  many  cases  approximate  results  are  sufficient. 
If  that  precaution  is  not  taken  it  may  happen  that  an  after- 
noon's work  will  be  wasted  because  of  some  fault  of  the 
material,  apparatus,  or  observer,  which  would  have  been  dis- 
covered immediately  the  first  test  was  worked  out. 

The  amount  of  time  on  each  experiment  varies  with  the 
individual  student.  It  is  usually  necessary  to  spend  a  good 
deal  of  time  upon  any  subject  of  which  it  is  desired  to  have 
a  full  knowledge.  The  student  should  not  consider  it  irksome 
or  unnecessary  to  repeat  experiments. 

While  a  multiplicity  of  experiments  may  be  very  attractive 
— especially  when  they  are  varied — yet  it  is  possible  that 
labour  which  appears  to  be  mere  drudgery  may  be  of  the 
greatest  educational  value.  There  is  a  great  deal  of  what 
people  who  possess  no  enthusiasm  for  their  work  call  drudgery 
in  the  life  of  the  engineer.  "  Staying  power "  is  often 
the  best  characteristic,  in  the  laboratory  or  in  the  works  of 
a  reliable  man. 

The  object  of  the  laboratory  is  not  to  pump  into  the  student's 
mind  a  large  amount  of  information,  but  to  cultivate  in  that 
mind  the  ability  to  reason,  to  plan  and  scheme  out  experiments. 
In  order,  however,  to  thoroughly  understand  underlying 
principles,  routine  work  must  be  done.  Originality  will  be 
useless  unless  combined  with  a  knowledge  of  fundamental 
laws.  Discipline  is  essential  in  the  laboratory,  as  elsewhere, 
and  the  student  must  subordinate  his  own  ideas  until  the 
opportunity  presents  itself  for  their  presentation. 


INTRODUCTION  o 

That  laboratory  instruction  is  essential  is  now  no  longer 
doubted.  The  equipment  in  all  of  the  centres  of  higher 
education  in  this  country  is  growing  each  year ;  in  some  it 
might  almost  be  called  magnificent.  The  whole  tendency  of 
the  work  is  to  arouse  interest.  It  appeals  to  the  eye  and  the 
sense  of  touch  in  a  way  impossible  to  obtain  in  the  class-room. 
In  the  University  of  London  Engineering -Examinations  (for 
internal  students)  marks  are  given  for  the  laboratory  work. 
There  is  a  growing  tendency  in  the  same  direction  in  the 
provinces.  Each  of  the  students,  who  takes  the  examination 
in  the  strength  of  materials,  presents  a  book  containing  a 
report  of  the  tests  which  he  has  made.  It  might  be  an  advan- 
tage if  the  laboratory  rough  note-book  were  also  inspected. 
In  any  case,  the  student's  ability  is  judged  from  his  record  of 
laboratory  instruction.  It  is  advisable,  therefore,  for  this  to 
be  neatly  compiled. 

At  the  end  of  this  book  is  a  chapter  dealing  with  the 
experiments  which  are  usually  undertaken  for  the  purposes 
of  these  examinations.  Those  actually  performed  must 
of  necessity  depend  upon  the  equipment  of  the  particular 
laboratory  in  which  the  student  is  working  and  the  time 
which  he  is  able  to  give  to  this  branch  of  study. 

Possibly  in  some  laboratories  opportunities  will  occur  for 
the  more  advanced  students  to  undertake  special  investiga- 
tions. It  is  suggested  that  some  of  the  researches  alluded  to 
in  this  book  may  serve  as  a  guide  to  that  end. 

The  Report  of  the  Test. — The  writing  up  of  the  report  of 
the  experiment  is  by  no  means  the  least  important  portion  of 
the  work.  Unfortunately,  very  few  people  express  their 
thoughts  in  an  intelligible  fashion.  There  are  men  of  great 
technical  ability  whose  writings  do  not  always  contain  clear 
expression  of  their  thoughts.  It  is  to  be  hoped  that  the 
twentieth  century  system  of  training  for  engineers  will  alter 
that  in  time.  Clear  expression  should  be  the  natural  outcome 
of  clear  thinking.  Every  engineering  student  will  be  called 
upon,  at  some  period  in  his  career,  to  furnish  a  report  upon 
a  technical  subject.  It  is  probable  that  the  report  will  be  read 


6  A  HANDBOOK  OF  TESTING  MATEEIALS 

by  those  who  know  little  or  nothing  of  technical  work.  The 
client  may  be,  for  instance,  a  solicitor,  banker,  financier,  or 
a  journalist.  He  will  be  influenced  by  the  manner  in 
which  the  report  is  written.  Most  of  us  who  have  to  write 
upon  technical  subjects  live  to  regret  that  we  had  but  little 
training  in  the  .art  of  composition  in  our  student  days. 
Lucidity  is  the  mental  lubricant  which  so  many  of  us  lack. 
In  writing  up  the  report  of  any  test  there  is  an  opportunity 
for  neatness  and  clearness  of  expression.  It  should  be  com- 
posed as  if  for  a  client  who  knows  nothing  whatever  about 
the  subject. 

There  is  a  great  temptation  to  occupy  considerable  space 
with  a  dissertation  upon  this  subject  of  writing  the  report. 
It  is  with  difficulty  resisted.  Let  the  student  remember  that 
a  shop  labourer  can  put  a  piece  of  material  in  the  testing 
machine  and  break  it.  It  requires  a  competent  engineer  to 
conduct,  and  report  upon,  a  test  such  as  is  needed  for 
commercial  purposes. 


CHAPTER  II 

GENERAL  PROPERTIES  OP  MATERIALS 

Ductile  and  Brittle  Materials. — The  materials  used  in 
engineering  work  are  roughly  divided  into  two  classes,  viz., 
ductile  and  brittle.  It  is  difficult  to  say  whether  some  materials 
should  be  considered  as  ductile  or  brittle,  as  there  is  no  decided 
line  of  demarcation.  The  past  history  of  the  material  will 
affect  its  properties. 

Ductility  may  be  defined  as  the  ease  with  which  a  metal  can 
be  elongated  into  a  wire  by  being  drawn  through  the  gradually 
diminishing  holes  of  the  wire-drawer's  plate.  In  general,  for 
testing  purposes,  we  call  a  material  ductile  when  it  stretches 
perceptibly  before  fracture  during  a  tension  test. 

A  gauge  of  this  property  called  ductility  is  supplied  if  we 
calculate  the  percentage  elongation  of  the  material,  and  also 
the  percentage  reduction  in  area  of  the  fracture,  after  the  test 
is  completed. 

We  can  group  together  a  number  of  metals  which  are  ductile. 
Steel,  the  material  most  generally  used  in  engineering  work, 
varies  considerably  in  composition  and  in  mechanical  proper- 
ties. There  is  the  steel  which  can  be  used  as  tie-rods  or  crank- 
shafts, and  there  is  the  steel  used  for  castings.  The  problem 
is  more  complicated  each  year  by  the  discovery  and  introduc- 
tion of  steel  alloys.  Again,  steel  and  its  alloys  are  extremely 
sensitive  to  mechanical  working  and  temperature  treatment. 
The  physical  properties  may  be  completely  changed  by  heating 
the  material  to  a  certain  temperature  and  cooling  slowly  or 
suddenly.  In  general,  we  may  say  that  the  steel  which  has  a 
low  carbon  constituent  is  ductile.  The  following  metals  are 
usually  classified  as  ductile,  viz.,  gold,  silver,  platinum,  iron,1 

1  Certain  types  of  iron  (including  steel  in  the  general  term  iron). 


8  A  HANDBOOK  OF   TESTING  MATERIALS 

nickel,  copper,  palladium,  aluminium,  zinc,  tin,  and  lead. 
Metals  which  stretch  imperceptibly  before  fracture  during  a 
tension  test  are  said  to  be  brittle.  In  general  such  metals  are 
very  strong  in  compression,  weak  in  tension,  and  unsuitable  to 
withstand  shock. 

The  properties  of  the  new  alloys  (which  are  constantly  being 
discovered)  are  in  many  cases  very  remarkable.  It  is  advisable, 
when  testing  any  material,  to  obtain  some  rough  idea  before 
commencing  the  test  as  to  its  mechanical  properties,  otherwise 
damage  to  the  instruments  or  shackles  may  result. 

Chemical  Analysis. — This  is  a  branch  of  the  subject 
which  the  average  college  student  has  little  or  no  time  to 
investigate.  The  skill  and  experience  necessary  for  an  exact 
and  reliable  analysis  of  steel  or  cast-iron,  which  are  by  far 
the  most  important  materials,  can  only  be  gained  by  long 
specialisation.  The  only  part  of  the  subject  which  it  is 
necessary  for  the  engineer  to  know  is  how  to  prepare  a  sample 
for  submitting  to  the  chemist.  This  should  be  done  as 
follows : — 

Preparing  Samples. — These  should  be  in  the  form  of  fine 
turnings  or  drillings,  but  not  dust.  They  must  be  perfectly 
free  from  all  oil  and  other  foreign  substances. 

Take  a  bar  specimen  and  commence  drilling  in  one  side 
with  a  flat  angled  drill  about  ^-inch  diameter.  When  the 
top  J  inch  has  been  removed,  shake  out  the  drillings  and 
prepare  to  make  a  proper  sample.  With  a  ^-inch  drill,  bore 
into  the  specimen  to  a  depth  not  exceeding  \  inch.  Repeat 
this  in  various  parts  of  the  bar,  and  collect  together  about 
2  or  3  ounces  of  fine  drillings.  These  should  be  at  once 
placed  in  a  clean  test-tube  or  sample  bottle,  and  handed 
on  to  the  chemist  who  will  carry  out  the  analysis. 

The  usual  iron  and  steel  analysis  will  give  as  percentages : 
carbon,  silicon,  sulphur,  phosphorus  and  manganese. 

Structure  of  Materials. — In  general,  the  appearance  of  the 
fractured  surface  of  a  bar  of  metal  is  an  index  of  its  character. 
An  easy  way  of  obtaining  some  idea  of  the  properties  of  the 
material  is  by  nicking  a  bar  on  one  side  with  a  chisel,  gripping 


GENERAL  PROPERTIES  OF   MATERIALS  9 

it  in  a  vice,  and  breaking  it  with  a  hammer.  The  brittleness 
or  toughness,  as  well  as  the  general  strength  of  the  material, 
is  indicated  by  the  angle  through  which  it  bends  and  the  force 
required  to  break  it.  The  appearance  of  the  fracture  should 
be  noticed  in  all  tests,  and  it  is  usually  advisable  to  record  it. 
The  bar  is  said  to  be  crystalline  when  made  up  of  visible 
crystals,  either  coarse  or  fine.  When  the  crystals  are  so  fine 
that  they  cannot  be  noticed  as  crystals  by  the  eye,  the  fracture 
is  said  to  be  granular.  Sometimes  the  grains  are  so  minute 
as  to  be  called  silky — as  is  the  case  with  a  tool  steel  properly 
hardened.  Wrought-iron  usually  shows  a  fracture  which  has 
the  appearance  of  the  material  breaking  piecemeal,  owing  to 
the  imperfect  adhesion  between  the  numerous  microscopic 
slag-fibres  and  the  iron  and  the  great  difference  in  the  tough- 
ness of  the  two  materials.  The  structure  is  called  fibrous. 
Generally  speaking,  a  coarsely  crystalline  or  granular  metal 
has  less  satisfactory  working  properties  than  one  of  the  same 
class  in  which  the  fracture  is  finer.  Incidentally,  it  may  be 
noted  that  the  size  of  the  grain  often  largely  depends  upon 
the  temperature  at  which  the  metal  was  cast,  and  upon  the 
subsequent  thermal  and  mechanical  treatment. 

The  Microstructure  of  Materials. — Although  the  examina- 
tion of  metals  under  a  microscope  is  a  matter  for  the  metal- 
lurgist rather  than  the  engineer,  this  branch  of  the  testing  of 
materials  has  become  of  such  importance  during  recent  years 
that  it  is  essential  that  the  engineer  engaged  in  the  testing 
of  materials  should  at  least  be  able  to  follow  the  methods 
employed  in  this  branch  of  metallography,  and  be  able  to 
judge  something  of  the  properties  of  a  material  from  micro- 
photographs  prepared  by  an  expert  in  that  particular  branch. 

Like  large  numbers  of  other  members  of  the  mineral 
kingdom,  the  metals  have  a  crystalline  structure,  formed  when 
the  metal  solidifies  or  is  subjected  to  certain  mechanical 
treatment.  In  the  impure  state  of  the  ordinary  materials  of 
construction,  this  crystalline  condition  is  changed  to  give 
a  peculiar  but  characteristic  appearance  to  the  material,  when 
examined  under  the  microscope.  This  depends  on  the  exact 


10  A  HANDBOOK  OF  TESTING  MATERIALS 

nature  of  the  impurities  and  on  the  previous  mechanical  and 
heat  treatment  to  which  it  has  been  subjected.  This  appear- 
ance is  termed  the  microstructure. 

The  specimens  to  be  examined  are  cut  from  the  material  to 
a  convenient  size  suitable  for  holding  in  the  fingers.  The 
piece  is  then  brought  to  a  smooth  surface  by  machining, 
grinding,  or  filling  and  smoothing  up  on  several  grades  of 
emery  cloth  glued  to  a  smooth  block  of  hard  wood.  The 
finishing  process  is  performed  by  polishing  on  a  revolving 
polishing  disc  covered  with  chamois  leather  to  which  a  small 
amount  of  jewellers'  rouge  has  been  applied. 

The  specimen  is  then  "  etched  "  with  a  dilute  acid  solution 
or  some  other  liquid  which  will  attack  the  metal  and  preferably 
stain  some  parts  different  from  others.  When  mounted  on  a 
microscope  and  illuminated  with  light  directed  normal  to 
its  surface  the  microstructure  is  clearly  exhibited  by  a  magni- 
fication of  from  30  diameters  upwards.  When  necessary  for 
the  purpose  of  keeping  records  photographs  can  be  taken  of 
the  image  by  attaching  a  special  form  of  camera  to  the  eye- 
piece. 

The  examination  is  most  important  in  connection  with  iron 
and  steel,  as  it  not  only  gives  a  rough  idea  of  its  composition, 
but  also  gives  to  the  expert  a  good  idea  of  the  heat  treatment 
which  the  steel  has  undergone  ;  a  point  which  it  is  obvious 
would  be  difficult,  if  not  impossible,  to  determine  by  chemical 
analysis.  Thus,  in  the  case  of  iron  containing  0*9  per  cent,  of 
carbon,  if  this  steel  is  properly  and  carefully  annealed  a 
uniform  product  results  known  as  pearlite,  and  when  examined 
under  the  microscope  is  observed  to  consist  of  either  uniform 
streaks  of  dark  and  light  lines  or  similar  granules,  and  derives 
its  name  from  the  play  of  colour  on  its  surface,  causing  a 
slight  resemblance  to  mother-of-pearl.  When  this  is  observed 
in  the  case  of  the  particular  steel  mentioned  it  shows  careful 
annealing.  On  the  other  hand,  if  this  same  sample  was 
raised  to  a  bright  cherry  red,  and  suddenly  quenched  in  a 
freezing  mixture  of  ice  and  salt,  i.e.,  an  exaggerated  case  of  bad 
heat  treatment  or  a  hardening  process,  the  structure  observed 


Fracture  of  specimen  tested  as  cast. 


Micrographs  of  Cast  Steel  before  and  after  annealing. 
Magnified  28'5  diameters. 


Specimen  tested  when  annealed  (no 
fracture). 


PLATE  I. 


GENERAL  PEOPERTIES   OF  MATERIALS 


11 


is  known  as  martensite,  and  takes  the  form  of  interlacing 
needles  quite  different  from  pearlite.  It  might  be  mentioned 
that  in  the  particular  case  we  have  chosen  the  martensite  is 
known  sometimes  as  hardenite,  and  is  observed  as  the 
principal  constituent  of  hardened  steel. 

Percentage  of   Carbon 


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0                     5                    10                    15                    20                   25                   30         °/ 
100                  95                   90                   85                   80                   75                   70        "/ 

FIG.  1. — Curves  showing  Effect  of  varying  Percentages  of  Carbon  in 
Steel  on  the  Tenacity,  Hardness  and  Ductility  of  the  Material. 

The  reason  for  these  differences  is  largely  due  to  the  fact 
that  (again  referring  to  the  particular  case  chosen)  when 
cooled  slowly  the  carbon  and  some  of  the  iron  combine  to 
form  what  is  considered  a  definite  compound  known  by  its 
appearance  in  the  microscope  as  cementite,  or  chemically  as 
iron  carbide  (Fe8C),  and  containing  6*67  per  cent,  of  carbon 
and  pure  iron,  known  in  microstructure  phraseology  as 
ferrite.  On  the  other  hand,  when^cooled  suddenly  the  steel 


12  A  HANDBOOK  OF  TESTING  MATERIALS 

forms  unsegregated  pearlite,  a  combination  of  iron  and  carbon 
containing  0*9  per  cent,  of  carbon  which  has  crystallised 
without  separating  into  carbide  and  ferrite.  In  this  connec- 
tion Howe  has  given  a  very  instructive  diagram  showing  the 
relation  between  the  varying  percentages  of  cementite  and 
ferrite,  such  as  occur  in  annealed  specimens  and  the  physical 
properties  of  the  material.  It  should  be  noted  that  unless  the 
specimen  is  annealed,  while,  of  course,  the  percentage  of 
carbon  will  remain  the  same,  the  percentage  of  cementite  will 
be  less.  Fig.  1,  taken  from  Howe's  work,  shows  the  effect  on 
tenacity,  hardness  and  ductility,  of  different  percentages  of 
carbon. 

When  the  percentage  of  carbon  is  large  (as  in  grey  pig-iron) 
very  slow  cooling  causes  the  carbon  to  separate  into  crystalline 
flakes,  distinguished  as  graphite,  and  is  observed  in  the 
microscope  obtruding  among  the  crystal  grains  of  ferrite. 
The  presence  of  sulphur,  phosphorus,  manganese,  and  silicon 
can  likewise  be  recognised  by  the  characteristic  appearance 
which  they  give  to  the  structure  depending  on  the  heat  treat- 
ment. Marked  changes  are  likewise  produced  in  the  non- 
ferrous  metals,  and  annealed  or  hardened  brass  can  be 
distinguished  at  a  glance  by  the  entire  change  of  its  crystalline 
nature. 

Plate  L,  prepared  from  drawings  and  photographs  kindly 
loaned  by  Dr.  J.  Arnold,  of  Sheffield  University,  will  illustrate 
in  a  striking  fashion  the  remarkable  change  brought  about  in 
cast  steel  by  annealing.  The  top  half  (as  cast)  illustrates 
martensitic  structure,  while  the  lower  half  (annealed)  illus- 
trates pearlite  structure.  The  change  in  mechanical  properties 
will  be  readily  seen  from  the  drawings  of  a  specimen,  one  bent 
before  and  the  other  after  annealing. 

Mechanical  Properties. —The  results  of  different  tests  made 
upon  various  materials  show  some  remarkable  contrasts.  It  is 
of  advantage  that  the  materials  do  not  all  possess  the  same 
properties,  and  it  is  obvious  that  while  one  material  may  be 
the  most  suitable  for  one  purpose,  it  is  quite  unsuitable  for 
another. 


GENERAL  PROPERTIES  OF  MATERIALS  13 

It  is  important  to  know,  for  any  material,  (a)  the  load  at 
which  it  ceases  to  be  elastic ;  (b)  the  maximum  load  before  or 
at  the  point  of  fracture.  In  commercial  testing  (a)  is  usually 
taken  as  that  load  at  which  a  large  amount  of  stretch  takes 
place  and  the  beam  drops.  This  point  is  usually  called  the 
yield  point.  In  scientific  testing  there  is  some  difficulty  con- 
cerning this  matter  of  elastic  breakdown,  and  there  are  in  use 
three  terms  which  require  explanation.  They  are  :— 

(1)  The  Limit  of  Proportionality. — This  is  usually  taken  as 
that  point  on  the  stress  strain  diagram  where  the  increase  in 
stretch  is  not  exactly  proportional  to  the  increase  in  load. 
Obviously  the  exact  point  at  which  this  takes  place  will  depend 
upon  the  sensitiveness  of  the  extensometer  used  to  detect  the 
stretch. 

(2)  The  Elastic  Limit. — If,  when  the  weight  is  run  back 
and   there   is   no   load   on   the   specimen,  the   extensometer 
pointer  returns  to  its  original  position  at  the  starting  of  the 
test,  there  is  said  to  be  no  permanent  set  upon  the  material. 
When  such  a  permanent  set  is  recorded  we  have  reached  the 
elastic  limit.     In  many  alloys  there  is  such  a  gradual  change 
from  the  elastic  to  the  plastic  state  that  it  is  essential  to  have 
some  other  criterion  than  the  drop  of  the  beam.     In  which 
case  it  is  usual  to  record  the  load  at  which  the  permanent  set 
is  a  certain  definite  amount,  such  as,  say,  TJ-Q  part  of  an 
inch. 

(3)  The  Yield  Point. — This  is  usually  taken  as  the  load  at 
which  the  drop  of  the  beam  is  first  noted. 

Mild,  or  low  carbon,  steel  usually  shows  all  three  points 
quite  distinctly.  At  the  critical  point  where  elastic  breakdown 
first  takes  place,  however,  the  influence  of  time  on  the  amount 
of  stretch  is  so  very  marked  that  it  seems  probable  that, 
under  ideal  conditions  of  loading  and  a  perfectly  homogeneous 
material,  all  three  points  would  coincide. 

In  the  practical  use  of  materials  the  three  characteristics — 
elastic  limit  (or  yield  point),  breaking  load,  and  extensibility- 
are  of  the  first  importance.  It  is  not  sufficient  to  know  what 
weight  a  bar  of  metal  will  withstand  without  rupture  ;  it  is  of 


14  A  HANDBOOK  OF  TESTING  MATERIALS 

the  utmost  importance  to  ascertain  what  load  it  will  bear 
without  sensible  distortion.  A  metal  which  must  be  shaped 
under  a  hammer  may  with  advantage  have  a  low  elastic  limit, 
so  long  as  its  extensibility  is  sufficient.  Such  a  metal  is 
usually  tough.  Hard  steel  is  very  strong,  but  its  extensibility 
is  slight,  and  the  hardest  kinds  are  liable  to  be  broken  under 
a  sudden  blow. 

The  Various  Tests. — Although  it  is  most  usual  to  determine 
the  tensile  strength  of  a  material,  it  is  being  gradually  recog- 
nised that  other  tests  are  also  essential.  If  a  material  is  to  be 
subjected  to  a  push  stress,  then  a  compression  test  is  the  most 
satisfactory.  Similarly,  if  a  material  is  to  be  used  in  a  shaft, 
where  it  is  subjected  to  a  twist,  a  torsion  test  should  be  made. 
At  present  there  is  no  law  for  all  materials  which  connects  the 
strength  in  tension  with  that  of  the  material  in  compression 
and  torsion.  It  is  quite  possible  to  imagine  a  bar  of  metal 
which  almost  resembles  a  bundle  of  straws.  It  would  be  per- 
fectly satisfactory  if  tested  in  tension,  but  fail  utterly  if  subjected 
to  torque  or  compression. 

It  often  happens  that  materials  are  subjected  to  alternating 
stresses  of  push  and  pull.  In  which  case  the  tests  which  reveal 
the  properties  suitable  for  such  work  are  the  alternating  stress 
tests  described  later.  Unfortunately  such  tests  usually  take  a 
considerable  time  to  carry  out,  and  are  therefore  not  generally 
conducted  for  commercial  purposes,  although  their  importance 
is  now  fully  recognised. 

Similarly,  materials  are  in  practice  frequently  subjected  to 
combined  loadings,  such  as  torsion  and  thrust  in  a  propeller 
shaft,  and  it  is  necessary  to  determine  the  loads  which  it  is 
possible  to  safely  carry.  Tests  made,  however,  under  such 
conditions  would  be  too  expensive  for  commercial  purposes, 
and  it  is  left  for  researches  to  determine  if  static  tests  will 
suffice  to  allow  us  to  estimate  the  loads  to  be  carried. 

Again,  it  happens  on  railways  that  the  steel  lines  are  sub- 
jected to  heavy  blows  or  to  suddenly  applied  loads.  In  tension, 
compression  bending,  or  torsion  tests  (or  static  tests,  as  they 
are  called)  the  load  should  be  applied  very  gradually  and 


GENERAL  PROPERTIES  OF   MATERIALS  15 

steadily  (any  irregularity  in  the  time  of  loading,  or  even 
irregularity  of  the  speed  at  which  the  load  is  applied,  will 
affect  the  results ;  hence  the  importance  of  adding  equal 
increments  of  load  during  equal  increments  of  time).  But 
frequently  materials  (such  as  those  used  for  rails  or  armour 
plate)  are  subjected  to  impact.  A  special  form  of  testing 
machine  is  used  for  such  tests. 

Therefore  the  reader  will  see  that  various  special  tests  are 
described  for  certain  materials,  and  while  the  actual  com- 
mercial value  of  such  tests  may  be  a  matter  for  discussion, 
there  can  be  no  two  opinions  as  to  their  advantage  for  a 
complete  experimental  study  of  the  properties  of  materials 
used  in  engineering  work. 


CHAPTEK  III 

MACHINES    FOR   TENSION,    COMPRESSION,    AND    BENDING    TESTS 

The  Usual  Machine. — It  is  the  usual  practice  to  build  a 
tensile  testing  machine  so  that  it  can  be  readily  adapted  to 
testing  materials  in  compression  or  bending.  Although  this 
"  omnibus  "  testing  machine  is  of  great  advantage  in  a  com- 
mercial laboratory,  since  it  saves  capital  outlay,  yet  it  is  some- 
times awkward  in  a  college  laboratory,  because  only  one  group 
of  students  can  be  at  work  doing  one  of  the  tests.  Although 
the  usual  size  of  testing  machine  in  colleges  is  from  50  tons 
to  100  tons,  it  is  possible  that  for  most  of  the  experimental 
work  done  by  the  student  a  10-ton  machine  is  large  enough, 
in  which  case  there  may  be  sufficient  capital  available  for  two 
or  even  three  machines.  However,  if  the  reader  grasps  the 
principles  of  the  "  omnibus "  machine,  he  will  understand 
those  used  only  for  one  of  the  tests.  The  above  tests  are 
enumerated,  but  it  will  be  seen  later  that  the  "  omnibus  " 
testing  machine  is  also  used  for  other  special  tests. 

Tensile  Testing  Machines. — The  easiest  way  of  obtaining 
the  tensile  strength  of  any  material  would  be  to  take  a  rod 
of  that  material,  suspend  it  in  a  vertical  position  from  one 
end,  and  hang  weights  on  the  other  end  until  it  breaks.  The 
aggregate  of  the  weights  suspended  at  that  moment  from  the 
free  end  would  form  the  breaking  load  for  that  particular  bar. 
The  cross-sectional  area  of  the  bar,  being  known,  the  break- 
ing stress  for  that  material  could  easily  be  deduced.  In  a 
similar  manner  the  compressive  or  bending  strength  could  be 
obtained.  But  this  simple  and  crude  method  of  obtaining  the 
strength  of  materials  could  only  be  used  where  the  bar  tested 
had  an  extremely  small  cross-section,  or  else  when  the  material 
itself  was  very  weak.  With  ordinary  materials,  such  as  are 


MACHINES  FOE  TENSION,   COMPKESSION,  ETC.          17 

used  in  engineering  practice,  this  method  could  not  be 
adopted,  as,  with  even  small  sizes  of  test  bar,  the  weights 
required  would  be  so  large,  and  the  labour  of  handling  them 
so  great,  as  to  render  its  use  in  ordinary  workshops  or  labora- 
tories a  practical  impossibility.  This  difficulty,  then,  is  over- 
come by  the  use  of  levers  interposed  between  the  point  of 
action  of  the  weight  and  the  specimen  whose  strength  we 
wish  to  determine.  The  interposition  of  this  lever,  or  set  of 
levers,  makes  the  use  of  a  smaller  weight  possible,  and  gives 
consequent  facility  in  handling  the  machine,  even  when  large 
powers  are  to  be  employed. 

We  will  now  sketch  out  a  very  simple  form  of  testing 
machine.  The  specimen  of  the  material  to  be  tested  consists 
of  a  truly  turned  cylindrical  bar,  one  end  of  which  is  gripped 
in  a  pair  of  jaws  fixed  to  the  framework  of  the  machine,  and 
the  other  attached  to  the  short  end  of  a  lever.  On  the  long 
arm  of  this  lever  a  weight  is  allowed  to  slide,1  so  that  its 
distance  from  the  fulcrum  can  be  varied  at  will.  We  com- 
mence with  the  weight  near  the  fulcrum,  so  that  little  or  no 
pull  is  exerted  on  the  specimen.  The  weight  is  then  run  out 
slowly  towards  the  end  of  the  arm,  the  load  being  thus 
gradually  applied  until  the  specimen  breaks.  The  breaking 
load  is  then  equal  to  the  weight  on  the  long  arm,  multiplied 
by  its  leverage,  or  by  the  ratio  between  the  long  and  short 
arms  of  the  lever.  But  here  we  encounter  another  difficulty. 
If  the  specimen  always  remained  of  the  same  length,  the  lever 
would  always  remain  of  the  same  effective  length,  as  it  would 
in  all  cases  be  horizontal.  But  on  the  application  of  a  load, 
the  specimen  stretches,  more  or  less,  according  to  the  nature 
of  the  material  that  is  being  tested.  The  lever  thus  assumes 
an  oblique  position  and  tends  to  bend,  as  well  as  to  stretch 
the  material.  It  is  necessary,  then,  to  take  up  the  stretch  in 
the  material  so  as  to  keep  the  lever  in  a  horizontal  position. 
This  is  usually  done  either  by  means  of  a  hydraulic  ram  or 

1  In  some  machines  the  weight  is  fixed  in  position  but  variable  in  amount.  The 
load  is  applied  by  adding  weights  at  the  end  of  the  long  arm  of  the  lever.  The 
same  result  is  obtained,  but  the  other  method  is  usually  employed  as  the 
application  of  the  load  is  thereby  made  more  uniform  and  gradual. 

T.M.  C 


18 


A  HANDBOOK  OF  TESTING  MATERIALS 


a  screw.  It  requires  no  great  effort  of  imagination,  now  that 
we  have  reached  this  point,  to  assume  that  the  hydraulic  ram 
or  screw  produces  the  pull  on  the  test  bar,  while  the  move- 
ment of  the  weight  along  the  lever  gives  us  a  method  of 
measuring  the  load  so  produced. 

There  are  two  principal  types  of  machine  used  for  testing 


Movable 
Jockey  Weight 


FIG.  2.— Diagrammatic  Sketch  of  Vertical  Type  Testing  Machine. 


materials  in  tension,  compression,  or  bending.  They  are 
termed  vertical  or  horizontal  machines,  according  as  the 
specimen  or  test  bar  is  placed  in  a  vertical  or  horizontal 
position.  A  diagrammatic  sketch  of  a  vertical  testing  machine 
is  shown  in  Fig.  2.  The  specimen  or  test  bar  A  is  held  in  a 
vertical  position  by  means  of  grips,  a  detailed  description  of 
which  will  be  given  later.  The  load  is  applied  by  means  of  a 
hydraulic  ram  C,  which  works  in  a  cylinder  B.  Water  or  oil 


MACHINES  FOE  TENSION,   COMPRESSION,  ETC. 


under  great  pressure  is  forced 
into  the  cylinder  B  and  causes 
the  ram  C  to  move  downwards. 
This  tendency,  however,  is  re- 
pressed by  the  specimen  A,  the 
tenacity  of  which  opposes  the 
load.  Owing  to  the  friction,  of 
the  cup  leathers,  which  are 
employed  to  prevent  the  water 
and  oil  from  leaking  past  the 
rarn,  the  pressure  of  the  oil  or 
water  in  the  cylinder  does  not 
give  us  a  true  measure  of  the 
load  on  the  specimen.  The 
upper  end  of  A  is  accordingly 
fastened  by  means  of  similar 
grips  to  the  shorter  arm  F  of  a 
lever  whose  fulcrum  is  fixed  at 
D.  On  applying  the  load,  the 
downward  tendency  of  F  is 
counterbalanced  by  running  the 
movable  jockey-weight  E  along 
the  longer  arm  of  the  lever 
(usually  called  the  "stillion"). 
The  length  of  the  "  stillion  "  is 
usually  so  calibrated  that  from 
the  position  of  the  weight  along 
this  arm  we  can  at  once  read  off 
the  load  on  the  specimen. 

The  horizontal  type  of  tester 
is  shown  in  Fig.  3.  In  principle 
it  is  precisely  the  same  as 
the  vertical  machine,  only  the 
arrangement  of  the  details  being 
different.  Here  the  specimen  A 
is  supported  in  a  horizontal 
position  and  the  load  applied  as 


c  2 


20 


A  HANDBOOK  OF  TESTING  MATERIALS 


MACHINES  FOB  TENSION,   COMPRESSION,  ETC.          21 

before  by  a  hydraulic  cylinder  B  and  ram  C.  The  lever  in 
this  case,  however,  instead  of  being  straight,  is  in  the  form 
of  a  "  bell  crank,"  as  it  is  now  desired  to  balance  the 
horizontal  pull  on  the  specimen  by  the  vertical  action  of  the 
weight  E. 

Wicksteed  Testing  Machine. — We  now  pass  on  to  consider 
some  of  the  more  important,  and  at  the  same  time  more 
complicated,  machines  used  for  testing  the  strength  of  the 
stronger  materials  (such  as  iron,  steel,  timber,  etc.),  in  tension, 
compression,  and  bending.  One  machine  can,  as  a  rule,  be 
adapted  to  test  all  these  properties  of  a  material,  though,  of 
course,  the  grips  used  and  the  kinds  of  specimen  employed 
differ  in  each  case.  The  principles  upon  which  the  Wicksteed 
machine  works  are  indicated  in  Fig.  4.  Water  or  oil  is  first 
admitted  into  the  compressing  cylinder.  This  consists  of  a 
hydraulic  cylinder  whose  ram  is  moved  backwards  and 
forwards  by  means  of  a  screw.  It  may  thus  be  described  as 
a  screw-driven  pump,  in  which  the  water  attains  a  very  high 
pressure  (2,000  to  3,000  Ibs.  per  square  inch).  This  water 
under  pressure  is  then  admitted  through  a  valve  into  the 
hydraulic  cylinder,  which  is  usually  secured  in  an  inverted 
position  to  the  base  of  the  main  frame  of  the  machine,  so 
that,  to  all  intents  and  purposes,  it  forms  an  integral  part  of 
the  latter.  Here  it  acts  downwards  on  the  ram,  the  pressure 
being  transmitted  through  the  lower  crosshead  to  the  adjusting 
screws,  and  thence  to  the  upper  crosshead  which  carries  the 
lower  grip  for  the  test  piece,  and  usually  slides  on  some  part 
of  the  framework  of  the  machine.  The  upper  grip  is  con- 
nected by  means  of  a  shackle  to  the  beam  through  a  knife 
edge.  The  beam  itself  usually  consists  of  two  wrought-iron 
plates  kept  apart  by  brackets  at  intervals,  though  sometimes 
it  is  made  of  cast-iron,  which  gives  greater  rigidity.  Between 
the  plates  two  steel  cylinders  are  fixed,  having  grooves  into 
which  the  hardened  steel  knife  edges  fit.  On  one  of  these  the 
beam  rests,  the  knife  edge  in  that  case  being  downwards.  On 
the  other  is  hung  the  upper  shackle  which  supports  the  test 
piece.  The  jockey  weight  is  usually  moved  along  the  beam  by 


22 


A  HANDBOOK  OF  TESTING  MATERIALS 


plate, 
and  is 


means  of  a  screw  which 
traverses  the  whole  length 
of  the  beam.  The  weight 
also  carries  a  vernier 
which  moves  along  a  scale 
fixed  to  the  beam,  so  that 
the  position  of  the  weight 
on  the  beam  can  be 
observed  with  great  exacti- 
tude. The  centre  of 
gravity  of  the  jockey 
weight  is  arranged  to  be 
as  nearly  as  possible  in 
an  exact  line  joining  the 
two  knife  edges,  as  if  this 
were  not  so  the  effect 
would  be  that  of  a  bent 
lever,  and  the  leverage 
would  alter  slightly  as  the 
beam  tilted  up  or  down. 
The  motion  of  the  beam 
in  this  direction  is,  how- 
ever, limited  by  stops  at 
the  free  end. 

The  object  of  the  ad- 
justing screws  is  to  enable 
the  distance  between  the 
grips  to  be  altered  to  suit 
the  length  of  the  specimen 
to  be  tested.  The  machine 
is  here  shown  fitted  up 
for  a  tensile  test.  If,  how- 
ever, a  compression  test 
is  required,  the  lower  grip 
is  replaced  by  a  square 
A  similar  plate  is  fixed  at  some  distance  below  this 
connected  to  the  same  point  on  the  beam  as  the  upper 


MACHINES  FOR  TENSION,   COMPRESSION,   ETC.          23 

shackle  in  the  tensile  test.  Consequently,  what  was  the  lower 
shackle  in  the  latter  test  is  now  the  upper  one,  and  vice  versa. 
If  now  the  cylindrical  test  piece  is  placed  between  these  two 
plates,  the  direction  of  stress  will  be  in  the  reverse  direction, 
and  consequently  the  material  will  be  compressed.  The  com- 
pression is  transmitted  to  the  beam  in  the  same  way  as  before 
The  Kennedy  Machine  (Fig.  5). — This  is  a  well-known 
testing  machine  of  the  horizontal  type.  The  ram  of  the 
hydraulic  cylinder  A  is  connected  to  a  cast-iron  sliding  frame 
B,  which  carries  an  adjustable  crosshead  C  in  which  are  fixed 
the  grips  for  receiving  one  end  of  the  test  bar.  The  other 
crosshead  D  is  fixed  between  two  screwed  bars  E  which 
traverse  the  whole  length  of  the  machine,  one  above  and  one 
below  the  hydraulic  cylinder.  If  a  tensile  test  is  to  be 
performed  the  specimen  is  gripped  between  these  two  cross- 
heads.  To  adjust  the  distance  between  them  the  key  which 
fastens  the  movable  crosshead  C  to  the  sliding  frame  is  drawn 
out,  the  crosshead  moved  to  the  required  distance,  and  the 
key  then  replaced.  The  frame  has  keyways  cut  in  it  at 
intervals  of  about  4  inches  to  allow  this  crosshead  to  be  fixed 
in  any  position.  For  compression  tests  a  flat  plate  is  provided 
at  that  end  (F)  of  the  sliding  frame  which  is  nearest  to  the 
ram,  and  a  similar  plate  on  the  fixed  crosshead  D,  the  specimen 
being  gripped  between  them.  The  screwed  rods  which  transmit 
the  stresses  to  the  levers  are  thus  always  in  tension,  the 
sliding  frame  being  similarly  invariably  in  compression.  The 
tension  is  transmitted  from  the  rods  to  a  back  crosshead  G, 
which,  through  knife-edges,  actuates  two  side  levers  H.  The 
power  being  applied  to  these  levers  at  a  point  above  the 
fulcrum  gives  the  effect  of  a  bell -crank  lever,  so  that  the 
direction  of  the  forces  is  changed  from  horizontal  to  vertical. 
This  is  invariably  the  case  with  horizontal  testing  machines, 
as  we  wish  to  balance  the  forces  by  means  of  a  sliding  weight, 
the  direction  of  whose  action  is,  of  course,  vertical.  The  outer 
ends  of  these  side  levers  are  connected  by  means  of  tension 
rods  K  to  the  short  arm  of  the  beam,  the  forces  being  measured 
by  running  out  a  jockey  weight  in  the  usual  way. 


24  A  HANDBOOK  OF  TESTING  MATEEIALS 

The  following   are   the  dimensions  of   a  50-ton  Kennedy 
machine  :  — 

Diameter  of  ram,  16'15  inches. 

Maximum  jockey  weight,  J  ton. 

Arms  of  bell-crank  lever,  3  inches  and  24  inches. 

Arms  of  beam,  8  inches  and  100  inches. 

q  Q  -j 

.*.  Total  leverage  of  machine  —     X       —       - 


.  •  .  Capacity  of  machine  —  50  tons. 

Since  the  scale  is  100  inches  long,  every  2  inches  of  travel 
represents  an  increment  in  loading  of  1  ton.  The  sliding 
weight  is,  however,  composed  of  cast-iron  discs  which  are 
removable,  so  that  for  smaller  powers  greater  accuracy  can  be 
obtained.  The  accumulator,  which  supplies  the  hydraulic 


^Spirit  Level 

Specimen 


/Hydraulic  Cylinder  Load 

FIG.  6. — Diagrammatic  Outline  showing  Principle  of  Werder  Machine. 

cylinder,  is  capable  of  giving  a  pressure  of  2,000  Ibs.  per 
square  inch.  It  is  fed  by  three  throw  pumps,  1^  inches  in 
diameter  with  3-inch  stroke.  These  are  driven  through  gear- 
ing by  a  three-phase  electric  motor  running  at  880  revolutions 
per  minute.  These  figures  are  given  with  the  intention  of 
conveying  to  the  reader  some  idea  of  the  actual  size  of  the 
principal  details  and  auxiliary  apparatus  of  a  machine  of  this 
capacity. 

The  Werder  Machine. — Although  not  used,  except  in  a 
modified  form,  in  England,  one  of  the  most  convenient  and 
accurate  machines  is  that  devised  by  Werder.  Fig.  6  indi- 
cates the  general  scheme  of  mechanism  employed,  the  action 
of  which  is  obvious.  It  will  be  seen  that  by  this  arrangement 
of  levers  it  is  possible  to  place  the  whole  of  the  controlling 
gear  at  one  end.  Hence,  specimens  of  any  desired  length  can 
be  tested  merely  by  extending  the  frame.  The  usual  length 


MACHINES  FOR  TENSION,   COMPRESSION,   ETC. 


for  which  these  machines  are 
built  is  30  feet.  Arrangements 
are  made  by  which  specimens 
can  be  tested  up  to  this  length 
in  both  tension  and  compression. 
Machines  on  this  pattern  have 
been  built  for  the  Government 
testing  laboratories  at  Berlin 
and  Munich,  for  the  polytechnic 
schools  at  Zurich  and  Vienna, 
and  for  several  manufactories 
and  railways.  It  was  on  a 
machine  of  this  type  that  most 
of  the  famous  researches  of 
Bauschinger  were  carried  out. 

It  should  be  clearly  under- 
stood that  the  diagrammatic 
scheme  illustrated  in  Fig.  6  is 
only  intended  to  illustrate  the 
general  principle  employed. 
For  details  of  the  methods 
employed  for  utilising  this  prin- 
ciple in  actual  practice,  the 
student  should  refer  to  the 
original  treatise  (in  the  German 
language)  given  below.1 

300-ton  Machine.— The  Civil 
Engineering  Department  of  the 
University  of  Birmingham  has 
the  privilege  of  possessing  a 
very  large  testing  machine.  It 
was  desired  to  carry  out  work 


1  Mittlieilungvn  a.  d.  Mechanixch- 
techniischen  Laboratorium  in  Miinchen, 
Heft  1  und  3.  Mascliine  zum,  Priifen  der 
Festigkeit  der  Materialien  und  Instruments 
zum  Messen  der  Gestaltsrerdnderung  der 
Proleltorper.  Miinchen,  1882. 


26  A  HANDBOOK  OF  TESTING  MATERIALS 

on  actual  structures.  The  smallest  capacity  of  a  machine  for 
this  class  of  work  was  fixed  at  300  tons.  There  was  some 
difficulty  in  preparing  a  specification  for  such  a  large 
size  machine.  Eventually  Messrs.  W.  and  T.  Avery,  Ltd., 
Soho  Foundry,  Birmingham,  were  commissioned  to  prepare 
and  submit  designs  for  such  a  machine,  and  a  machine  of 
700,000  Ibs.  capacity  was  finally  constructed  by  them  and 
installed  in  the  laboratory. 


FIG.  8. — End  View  of  300-ton  Birmingham  Testing  Machine. 

The  following  details  will  give  the  reader  an  idea  of  the 
general  design : — 

Leading  dimensions:  Maximum  length  for  tension,  28  feet; 
maximum  length  for  compression,  30  feet ;  span  for  bending, 
20  feet.  The  over-all  dimensions  of  the  machine  are :  Total 
length,  f>7  feet  9  inches;  maximum  height,  13  feet  3  inches; 
width  varying  from  7  feet  to  21  feet.  The  wedge-grips  can 
take  specimens  3-f  inches  in  diameter,  or  6  inches  by  2£  inches 
flat. 


•a 


28  A  HANDBOOK  OF  TESTING  MATERIALS 

General  arrangement :  The  machine  is  of  the  horizontal 
type,  with  the  ram  at  one  end  and  the  lever  system  and 
operating  platform  at  the  other.  Figs.  7  and  8,  on  pages 
25  and  26,  show  the  general  arrangement,  the  former  being 
a  front  elevation,  and  the  latter  an  end  elevation.  In 
Fig.  7  the  massive  cast-iron  bed  X  X  of  the  machine  is  ter- 
minated at  each  end  by  a  rigid  vertical  standard.  The  tops  of 
the  standards  are  connected  by  two  horizontal  columns  Y  Y, 
spanning  the  distance  between  them  without  intermediate 
support.  Thus,  for  the  whole  of  the  length  of  the  machine 
occupied  by  a  specimen  under  test,  there  is  a  clear  space  of 
2  feet  9  inches  at  the  sides  and  a  clear  space  of  3  feet  9  inches 
visible  from  the  platform  on  the  top.  The  latter  is  not  only 
important  because  it  enables  the  operator  to  watch  the 
specimen,  but  also  because  it  enables  heavy  specimens  to  be 
lowered  into  the  machine  by  the  overhead  traveller.  To  one 
vertical  standard  is  fixed  the  hydraulic  cylinder,  and  to  the 
other  the  lever  system.  Fig  9,  on  p.  27,  is  a  diagrammatic 
view  of  the  steelyard  mechanism,  and  Fig.  10,  on  p.  29,  of  the 
main  and  return  rams. 

Straining  mechanism :  The  machine  is  operated  by  hydraulic 
pressure,  two  supplies  of  water  being  available :  the  town 
pressure,  of  about  100  Ibs.  per  square  inch,  for  preliminary 
operations  and  adjustment ;  and  the  accumulator  supply,  of 
1,000  Ibs.  per  square  inch.  The  ram  L  is  2  feet  8  inches  in 
diameter,  giving,  with  the  low-pressure  supply,  a  total  thrust 
of  35  tons,  and  with  the  1,000  Ibs.  per  square  inch  the  full 
700,000  Ibs.  The  stroke  of  the  ram  is  5  feet  6  inches.  The 
main  cylinder  is  bolted  to  the  standard,  and  thus  forms  part 
of  the  frame  of  the  machine,  and  the  main  ram  is  hollow 
and  forms  a  cylinder  moving  over  a  fixed  subsidiary  ram  M 
1  foot  8  inches  in  diameter.  The  object  of  this  arrangement  is 
to  provide  for  the  return  of  the  main  ram  after  a  test.  Water 
from  the  low  pressure  supply  is  admitted  behind  the  fixed 
rani,  and  the  main  ram  is  driven  back  into  its  cylinder.  To 
the  head  of  the  main  ram  are  fixed  four  racks  N  sliding  in 
grooves  in  the  frame  of  the  machine,  and  notched  throughout 


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;j()  A  HANDBOOK  OF  TESTING  MATEETALS 

their  length  to  permit  of  the  travelling  crosshead  No.  2  being 
keyed  to  them  in  any  desired  position,  according  to  the  length 
of  the  specimen  under  test.  The  travelling  crosshead  is  moved 
by  means  of  gearing,  terminating  in  a  handle  at  each  side. 
Thus  the  load  on  the  ram  is  transmitted  to  the  sliding  racks, 
thence  to  the  crosshead  2  fixed  to  them,  and  from  the  cross- 
head  through  a  spherical  seating  to  the  specimen.  The  other 
end  of  the  specimen  is  held  by  one  of  the  floating  crossheads 
1  and  3,  according  to  the  character  of  the  test.  Between 
crosshead  2  and  crosshead  3  the  specimen  is  in  compression ; 
or  if  the  bending  beam  is  in  position,  the  load  on  the  beam  is 
transmitted  to  crosshead  3.  Between  crosshead  2  and  cross- 
head  1  the  specimen  is  in  tension.  The  floating  crossheads  1 
and  3  are  suspended  on  knife-edges  on  the  top  of  the  frame, 
and  are  connected  together  by  four  tension  rods  P,  the  whole 
arrangement  forming  a  floating  frame.  When  crosshead  3  is 
in  use — i.e.,  in  bending  and  compression  tests — these  rods 
transmit  the  load  to  crosshead  1,  and  hence  to  the  lever 
system.  The  connecting  link  between  the  floating  frame  and 
lever  system  is  the  main  link  B  B,  terminating  in  a  steel 
bearing-block  Q  Q,  which  engages  with  the  upper  knife-edge 
of  the  first  or  bell-crank  lever. 

Weighing  or  recording  mechanism  :  This  consists  of  a  main 
bell-crank  lever  A  A,  with  its  principal  knife-edge,  5  feet  long, 
engaging  with  a  plate  fitted  in  a  recess  in  the  bed.  The  load 
is  brought  on  to  a  similar  knife-edge  (forming  with  the  main 
knife-edge  the  short  vertical  arm  of  the  bell-crank)  directly  by 
the  main  link  B  B.  The  second  lever  C  C,  Fig.  8,  and  the 
final  lever  or  steelyard  D  D  run  at  right  angles  to  the  axis  of 
the  machine.  The  former  has  its  fulcrum  on  a  short  column  E 
fixed  to  the  bed  of  the  machine,  and  the  load  from  the  end  of 
the  long  arm  of  the  bell-crank  lever  is  transmitted  to  it 
through  side  links  G  G  and  a  cross-shackle  F.  The  steel- 
yard has  its  fulcrum  on  a  special  column  H  on  the  right  hand 
of  the  machine.  The  steelyard  carries  seven  poises,  each 
of  which  at  the  end  of  its  run  represents  100,000  Ibs.  on  the 
specimen.  Thus,  whatever  the  total  load,  1  inch  on  the  steel- 


MACHINES  FOR  TENSION,   COMPRESSION,   ETC.          31 

yard  scale  always  represents  the  same  increment  of  load.  At  the 
same  time,  there  are  no  loose  weights  to  put  on  or  take  off. 
The  poises  can  be  made  to  slide  over  or  back  along  the  steel- 
yard by  hand,  or  they  may  be  put  into  gear  with  a  screw,  and 
moved  by  hand- wheels  J. 

The  machine  is  operated  from  a  raised  platform  at  the 
steelyard  end ;  the  supply  and  exhaust  pipes  are  brought  to 
an  operating  valve  on  this  platform,  and  the  load  can  be  taken 
on  or  off,  the  steelyard  balanced  and  the  load  recorded  by  a 
single  operator  on  this  platform,  who  is  also  able  to  see  the 
specimen  under  test.  It  would  have  been  a  great  loss  to  the 
equipment  had  this  unique  machine  been  omitted.  The  great 
amount  of  research  work  possible  with  it  is  obvious  to  every 
engineer. 

The  author  is  indebted  to  Professors  Stephen  Dixon  and 
F.  H.  Hummel  for  the  above  particulars  and  drawings,  and 
to  the  editor  of  Engineering  for  the  photograph  of  the  machine 
given  in  the  frontispiece. 

Avery  Testing  Machine. — The  following  specification  of  a 
100-ton  machine  is  supplied  by  this  firm  and  describes  its 
construction  in  great  detail.  A  novel  feature  is  the  adoption  of 
double  acting  in  the  hydraulic  cylinder,  the  other  points  being 
very  similar  to  those  of  the  Kennedy  machine.  This  is 
included  as  an  example  of  how  such  a  specification  should 
be  drawn  up  as  well  as  with  the  object  of  familiarising  the 
reader  with  the  principles  of  design  adopted  by  this  firm. 

SPECIFICATION  OF  HORIZONTAL  TESTING  MACHINE. 

To  test  specimens  in  tension,  compression,  bending  and  shearing. 

Maximum  testing  capacity          .         .  .         .     100  tons. 

Longest  specimen  in  tension 12  feet. 

Longest  specimen  in  compression        .         .         .         .15  feet. 
Longest  beam  for  transverse  test         .         .  15  feet. 

This  machine  is  designed  specially  for  the  testing  up  to  100  tons  strain 
of  full-size  members  to  destruction.  It  consists  generally  of  a  hydraulic 
cylinder  and  ram  having  a  stroke  of  3  feet  6  inches,  forming  the  straining 
portion,  and  a  system  of  compound  levers  forming  the  weighing  or 
recording  portion.  The  hydraulic  supply  is  derived  from  the  town  main 
supply.  • 


32  A  HANDBOOK  OF  TESTING  MATERIALS 

The  straining  portion  of  the  machine  consists  of  a  heavy  section  double- 
acting  hydraulic  cylinder  of  special  design.  The  main  cylinder,  which  is 
a  heavy  casting,  has  a  large  hollow  ram.  which  slides  over  a  smaller 
stationary  ram. 

The  working  pressure  may  vary  from  850  Ibs.  to  1,120  Ibs.  per  square 
inch  and  the  diameter  of  the  larger  ram  is  of  such  dimensions  that  the 
tester  will  give  100  tons  strain  with  the  minimum  pressure.  The  cylinder 
is  accurately  bored,  and  the  rams  are  both  turned.  The  cylinder  is 
provided  with  the  usual  hydraulic  leathers,  secured  in  position  by  a 
turned  and  faced  cast-iron  cover  bolted  to  the  cylinder  flange. 

The  main  ram  is  fitted  into  a  massive  cast-steel  head,  into  which  the 
turned  and  screwed  ends  of  the  straining  racks  are  secured  by  means  of 
turned  and  screwed  nuts.  These  straining  racks  are  four  in  number,  and 
are  of  mild  steel  and  run  the  whole  length  of  the  bed.  They  are  for  the 
greater  part  of  their  length  rectangular  in  section,  terminating  in  round 
ends  where  they  pass  through  the  ram  head.  Machined  slots  are  pro- 
vided at  intervals  of  9  inches  to  receive  the  main  crosshead.  Four  nuts 
are  screwed  on  to  the  straining  racks  where  they  pass  through  the 
cylinder  flange,  and  these  allow  of  the  ram  being  locked  at  any  position 
of  its  stroke,  allowing  specimens  to  be  placed  under  a  strain  for  an 
extended  period. 

The  main  ram  is  copper-plated  to  prevent  corrosion. 

The  hydraulic  cylinder  is  turned  outside  and  fitted  in  a  heavy  casting, 
which  is  bored  to  receive  it.  This  casting  stands  upon  the  ground,  and 
to  it  are  bolted  the  four  cast-iron  columns  in  which  the  straining  racks 
slide.  These  columns  are  planed  between  the  castings  supporting  the 
hydraulic  cylinder  and  the  casting  against  which  the  pull  upon  the  main 
lever  fulcrum  is  received.  They  each  have  a  machined  groove  or  slot  to 
act  as  guides  to  the  straining  racks,  and  their  ends  are  all  faced. 

A  substantial  cast-steel  crosshead  runs  upon  wheels,  and  is  arranged 
to  be  capable  of  being  placed  in  any  position  in  the  straining  racks ; 
machined  slots  are  provided  at  the  top  and  bottom  of  the  crosshead  into 
which  loose  keys  are  inserted  to  connect  the  same  to  the  straining  racks. 
This  crosshead  is  made  hollow  to  receive  on  the  one  side  the  special 
holders  for  the  tension  test  and  on  the  other  side  the  adjustable  plattens 
for  testing  columns  in  compression. 

The  holders  for  the  tension  test  are  inserted  at  the  back  of  the  cross- 
head  and  have  spherical  seatings  to  give  true  alignment  to  the  specimens. 
These  holders  will  allow  of  any  of  the  recognised  forms  of  specimen 
being  tested.  Headed  specimens  are  secured  in  split  collars,  while  other 
types  of  specimens  are  secured  in  hardened  steel  wedge  grips. 

The  plattens  for  testing  columns  are  also  provided  with  spherical  seatings. 

The  weighing  or  indicating  portion  consists  of  a  very  heavily -constructed 
main  lever,  the  sides  of  which  are  mild  steel  plates.  Hardened  steel 
knife-edges  are  fitted  into  these  plates,  and  these  backed  by  means  of 
machined  mild  steel  blocks  acting  as  distance  pieces.  The  knife-edges 


MACHINES  FOE  TENSION,   COMPEESSION,  ETC.          33 

are  of  the  best  quality  steel  hardened,  and  are  arranged  to  be  1  inch  in 
length  for  every  5  tons  of  strain. 

The  bearings  are  all  of  hardened  steel,  the  fulcrum  bearing  being  fitted 
into  a  cast-iron  pedestal  on  the  main  casting.  The  weight  of  the  lever  is 
supported  by  means  of  wrought-iron  links,  with  hardened  steel  bearings, 
from  a  cast-iron  cross-beam  resting  upon  short  columns  which  are  bolted 
down  to  the  cast-iron  base  plate. 

The  main  knife-edges  of  the  levers  bear  in  a  hardened  steel  bearing- 
block  contained  in  a  projecting  verge  which  is  bolted  to  a  massive  cross- 
head  secured  to  the  main  tension  rods.  Two  other  crossheads  are 
attached  to  these  rods,  and  the  whole  floating  frame  of  three  crossheads 
and  two  tension-rods  are  suspended  from  cast-iron  pedestals  upon  the 
main  frame  by  means  of  wrought-iron  links  having  hardened  steel 
bearings. 

The  steelyard  is  a  massive  iron  casting,  fitted  with  hardened  steel  knife- 
edges  arranged  to  be  1  inch  in  length  for  every  5  tons  of  strain.  Its 
fulcrum  knife-edge  rests  upon  a  hardened  steel  bearing  fitted  into  a  cast- 
iron  pedestal  bolted  down  to  the  main -column. 

The  steelyard  is  traversed  by  three  poises,  which  are  connected  or 
disconnected  at  will  to  a  central  screw. 

When  tests  below  25  tons  are  required  the  first  poise  is  used  indepen- 
dently of  the  other  two  and  gives  readings  from  zero  up  to  2o  tons,  the 
1-ton  mark  being  8  inches  apart  and  the  sub-divisions  being  TfiW 
of  a  ton.  For  tests  between  25  and  50  tons  the  first  and  second  poises 
are  coupled  together,  and  these  now  give  readings  from  zero  up  to  50 
tons,  the  1-ton  marks  being  4  inches  apart,  the  sub-divisions  being 
TTRH7  °f  a  ton.  For  tests  between  and  50  and  100  tons  all  three  poises  are 
coupled  together,  and  readings  from  zero  up  to  100  tons  are  obtained,  the 
1-ton  marks  being  2  inches  apart,  and  the  sub-divisions  in  this  case 
being  J^TJ-  °f  a  ton.  All  the  finer  sub -divisions  are  obtained  by  means 
of  verniers  upon  the  poises. 

The  poises  are  propelled  by  a  hand- wheel  at  the  front  of  the  tester, 
this  being  connected  by  means  of  gearing  to  the  central  screw. 

This  arrangement  of  poises  secures  that  neither  of  the  poises  need  to 
be  removed  from  the  steelyard. 

A  carrier  and  buffer  spring  are  provided  to  lessen  the  shock  upon  the 
steelyard  when  the  specimen  breaks. 

The  steelyard  is  connected  to  the  main  lever  by  means  of  wrought- 
iron  links  having  hardened  steel  bearings. 

Tension  test. — Seven  pairs  of  hardened  steel  wedge  grips  are  supplied 
with  the  machine  to  enable  flat  and  round  specimens  to  be  tested  in 
tension.  The  maximum  length  of  specimen  in  tension  is  12  feet,  and  this 
specimen  can  be  tested  without  the  removal  of  the  cross-beam. 

Compression  test. — Columns  up  to  15  feet  in  length  and  of  a  maximum 
section  of  12  inches  diameter  can  be  tested  without  removing  the  cross- 
beam used  in  the  bending  test. 


34  A  HANDBOOK  OF   TESTING  MATERIALS 

Bending  or  transverse  test. — This  test  is  made  by  means  of  a  heavy  steel 
cross-girder,  consisting  of  rolled  steel  joists  having  steel  plates  riveted 
to  their  flanges.  A  cast-iron  grooved  track  is  bolted  to  the  plates  of  the 
cross-girder,  and  this  is  traversed  by  two  pedestals,  each  containing  a 
hardened  steel  hemi-cylindrical  bearing  block.  These  pedestals  can  be 
quickly  adjusted  to  any  desired  span  to  a  maximum  of  15  feet,  by  the 
movement  of  hand-wheels  at  the  ends  of  the  cross-girder. 

A  presser  foot  which  has  two  hemi-cylindrical  bearing  blocks  is  fitted 
into  the  movable  crosshead  in  place  of  the  platten  for  the  compression 
test,  and  this  bears  centrally  on  the  beam  being  tested. 

The  cross-beam  is  arranged  to  be  easily  removed.  To  facilitate  this  a 
carriage,  running  free  upon  wheels  and  having  side  rollers,  is  provided. 
To  centralise  the  beam,  projecting  pieces  upon  it  are  allowed  to  clip  at 
each  side  of  a  projecting  boss  upon  the  end  crosshead. 

Shearing  test. — This  apparatus  consists  of  two  cast-iron  portions  which  are 
guided  and  slide  in  one  another.  One  portion  is  bolted  to  the  casting  at 
the  front  of  the  steel  cross-beam,  and  to  this  the  specimen  is  clamped  by 
means  of  cross-plates  and  set  pins. 

The  other  casting  envelops  the  specimen,  against  which  it  is  forced  by 
means  of  the  straining  crosshead  of  the  machine. 

Both  portions  of  the  shearing  apparatus  are  provided  with  hardened 
steel  tools  to  give  the  shear.  The  whole  apparatus  is  strongly  constructed 
and  well  finished. 

An  absolutely  pure  shearing  test  is  given  by  means  of  this  apparatus.1 

The  general  design  of  the  machine  is  arranged  to  give  easy  access  to 
the  ram  head  for  the  removal  of  the  hydraulic  leather  packing. 

The  straining  racks  are  always  in  tension  and  are  secured  from 
deflection  due  to  their  own  weights  by  the  insertion  of  machined  strips. 
The  floating  frame  is  suspended  by  means  of  links  having  hardened  steel 
bearings. 

Amsler  Testing  Machine  (Fig.  11). — This  machine  differs 
from  any  that  we  have  hitherto  mentioned  in  the  fact  that  no 
beam  or  weight  is  used  to  measure  the  load  on  the  specimen. 
Great  care  is  taken  in  machining  the  cylinder  A  and  its  ram,  to 
ensure  a  perfect  fit  between  the  two,  so  that  no  cup  leather,  or 
other  packing,  is  necessary  to  prevent  leakage.  The  friction  at 
this  point  being  eliminated,  the  pressure  inside  the  cylinder 
may  be  taken  as  a  measure  of  the  load  on  the  test  bar.  Oil  is 
forced  from  the  compressing  cylinder  B  into  the  hydraulic 

1  This  statement,  made  by  the  makers,  must  be  understood  to  mean  pure 
shear  as  far  as  it  is  possible  to  obtain  it  without  the  very  special  means 
described  in  the  section  on  compound  stress. 


MACHINES  FOR  TENSION,   COMPRESSION,  ETC.          35 

cylinder  A,  where  it  does  work  on  the  specimen.  The  pressure 
from  A  is  transmitted  by  means  of  a  pipe  D  to  the  cylinder  C. 
As  this  pressure  is  necessarily  very  high,  no  mercury  column 
of  convenient  height  can  be  utilised  at  this  point  to  record  it. 
Accordingly  it  is  made  to  act  on  the  ram  E  which  actuates  the 
plunger  G.  This  combination  forms  a  reducer  (which  is 
exactly  the  opposite  of  an  intensifier),  for,  since  the  rod  and 
plunger  E  and  G  are  in  equilibrium,  it  follows  that  the  total 


FIG.  11. — Amsler  Testing  Machine  for  Short  Compression  Specimens. 

downward  pressure  on  E  is  equal  to  the  total  upward  pressure 
on  G.  Now,  since  G  is  much  larger  than  E,  the  pressure  per 
square  inch  on  G  must  therefore  be  much  less  than  that  on  E  ; 
in  fact,  the  pressures  per  square  inch  in  C  and  F  will  be 
inversely  as  the  areas  of  E  and  G.  The  plunger  G  presses 
downwards  on  a  layer  of  oil,  the  pressure  of  which  is  balanced 
by  that  of  a  column  of  mercury  H,  which  is  calibrated  to  read 
directly  the  load  on  the  specimen. 

In  some  cases,  however,  the  maximum  power  of  the  machine 
is  not  required,  so  that  greater  accuracy  in  reading  the  loads 
on  the  specimen  is  desirable.  The  ratio  of  reduction  is  then 

D  2 


36  A  HANDBOOK  OF  TESTING  MATERIALS 

made  less  by  the  following  device  :  Oil  is  pumped  into  the 
chamber  F  by  means  of  the  hand  pump  K  from  the  reservoir 
L.  In  this  way  the  plunger  G  is  raised  until  the  sleeve  M 
comes  into  contact  with  the  ring  N  and  raises  it  off  its  seating. 
The  oil  in  C  is  now  pressing  not  only  on  the  ram  E,  but  also 
on  the  annulus  N,  which  surrounds  it,  thus  enlarging  the 
effective  area  of  E.  This,  of  course,  has  the  effect  of  raising 
the  total  load  on  the  top  piston  and,  consequently,  that  on 
the  bottom  one  G.  Thus  the  pressure  in  F  is  more  nearly 
equal  to  that  in  C  than  was  before  the  case  ;  the  mercury 
column  H  is  made  longer,  and  thus  more  sensitive  to  the  rise 
in  pressure  in  the  main  cylinder  A.  In  fact,  the  arrangement 
is  equivalent  to  an  enlargement  of  the  scale  of  loading.  To 
eliminate  friction  as  far  as  possible  in  the  reducer,  the  plunger 
and  piston  are  given  a  backward  and  forward  rotation  by 
means  of  linkwork  actuated  from  the  main  compressor.  The 
specimen  to  be  tested  is  placed  between  the  two  tables  0  and  P, 
adjustment  for  length  being  effected  by  the  screw  and  hand- 
wheel  Q. 

Richie*  Testing  Machine  (Fig.  12). — In  the  Riehle  machine 
we  again  revert  to  the  jockey  weight  and  lever  as  a  method  of 
measuring  the  force  exerted  on  the  test  bar.  The  loading 
mechanism  in  this  case,  however,  consists,  not  of  a  cylinder 
and  ram,  as  in  previous  machines,  but  of  two  strong  screws 
D  and  E,  which  pass  vertically  up  the  machine.  These  screws 
are  rotated  (through  gearing  which  permits  of  several  speeds 
being  used)  by  an  electric  motor,  and  pass  freely  through  the 
bed  of  the  frame.  The  specimen  A  is  held  by  clips  to  the 
framework  B  and  the  table  C.  The  latter  is  moved  either 
upwards  or  downwards  by  rotating  the  screws  D  and  E,  on 
which  it  fits  like  a  nut. 

The  whole  of  the  framework  B  rests  on  a  system  of  levers 
to  which  the  load  on  the  specimen  is  transmitted  through 
knife-edges  at  F  and  G.  The  final  balance  is  effected  by  the 
jockey  weight  H,  which  moves  on  the  graduated  stillion  arm  K. 
It  can  easily  be  shown  that  the  pull  P  in  the  connecting 
rod  M  L  does  not  depend  011  the  relative  loads  on  F  and  G, 


MACHINES  FOE  TENSION,   COMPEESSION,  ETC. 


c 


O-4 


60 


but  merely  on  the  total  load  on  the  knife-edges.  Conse- 
quently, if  the  specimen  is  un  symmetrically  placed  in  the 
grips,  the  accuracy  of  the  machine  will  not  be  affected. 

In  machines  of  this  type  as  actually  built  there  are  several 


38 


A  HANDBOOK  OF  TESTING  MATERIALS 


special  features.  Placed  between  the  main  driving  pulley  and 
the  vertical  screws  is  a  system  of  change  gears,  controlled  by 
three  levers  and  a  hand-wheel.  One  lever  works  the  reverse 
while  each  of  the  other  controllers  give  two  speeds,  and  by 
varying  the  combination  of  these  four  levers  we  can  get  eight 
speeds  forward  or  reverse  (i.e.,  tension  or  compression).  The 
top  speed  is  generally  only  used  for  setting  the  machine.  For 


TbSnilior 


FIG.  13. — General  Arrangement  for  Girder  Testing. 

rapid  commercial  testing  it  is  also  desirable  to  fit  change  speed 
pulleys  on  the  driving  shaft,  or  use  a  variable  speed  motor. 
By  this  means  the  machine  can  be  set  or  changed  over  from 
a  tension  test  to  a  compression  test  in  a  few  minutes  without 
any  manual  labour  on  the  part  of  the  experimenter.  These 
machines  are  almost  invariably  fitted  with  autographic 
apparatus,  and  the  whole  can  be  made  entirely  automatic  by 
the  means  described  on  page  42.  One  excellent  feature  of 
this  type  of  machine  is  that,  as  the  experimenter  stands  at  the 
levers,  specimen,  poise  reading,  autographic  diagram,  and  all 


MACHINES  FOE  TENSION,   COMPRESSION,  ETC.          39 

the  controlling  levers  can  be  seen  or  regulated  without  moving 
his  position.  It  may  be  added  that,  since  to  develop  the 
full  advantages  of  this  machine  the  whole  is  run  as  fast  as 
possible,  there  is,  of  course,  a  liability  for  an  inexperienced 
experimenter  to  smash  some  of  the  gears  by  changing  speed 
carelessly.  In  fact,  considerable  experience  is  necessary  to 
manipulate  everything  in  the  best  possible  manner.  It  is 
sometimes  urged  against  this  type  of  multilevel*  machine  that 
wear  and  friction  are  likely  to  cause  greater  inaccuracies  than 
in  single  lever  machines. 

Arrangement  of  Machines  for  Bending  Tests. — All  the 
machines  hitherto  described  can  be  used  for  tension,  com- 
pression, or  bending  tests.  Fig.  13  shows  the  arrangement  of  a 
vertical  testing  machine  for  testing  girders,  etc.,  in  bending. 
Connected  with  the  stillion  knife-edge  by  means  of  four  tie  rods 
A  and  B,  is  a  table  C,  with  a  flat  machined  face.  Two  knife- 
edges  D  and  E  are  bolted  to  this  table  in  such  a  way  that  their 
distance  apart  can  be  adjusted  to  suit  any  size  of  specimen 
within  the  limits  of  the  machine.  These  knife-edges  often 
rest  on  spherical  seats,  which  adjust  themselves  as  the  load  is 
applied,  so  that  the  supporting  forces  are  exactly  vertical  in 
direction.  The  specimen  to  be  tested  rests  symmetrically 
across  these  knife-edges,  and  is  loaded  at  the  centre  by  means 
of  a  knife-edge  F. 

The  ram  L  is  forced  downwards  by  the  water  in  the 
hydraulic  cylinder,  and  the  load  transmitted  by  means  of 
tension  bars  H  and  K  to  the  knife-edge  F. 

Horizontal  machines  can  be  adapted  to  take  specimens  for 
bending  in  a  similar  manner.  They  are  not,  however,  so 
convenient  for  testing  large  specimens  as  the  vertical  type  of 
machine,  as  in  the  latter  the  girder  rests  by  its  own  weight  on 
the  supporting  knife-edges,  while  in  the  horizontal  machine  it 
has  to  be  supported  in  position  by  the  central  load. 

Bailey  Transverse  Testing  Machine. — A  simple  machine 
for  testing  the  transverse  strength  of  a  beam  is  that  made  by 
W.  H.  Bailey  &  Co.,  Ltd.,  which  has  a  capacity  of  40  cwt. 
The  load  is  applied,  as  in  the  case  of  ordinary  testing  machines, 


MACHINES  FOE  TENSION,   COMPEESSION,  ETC.          41 

by  means  of  a  lever  and  sliding  weight.  The  test  bar  is  sup- 
ported at  the  ends  in  two  blocks,  which  have  knife-edges 
pointing  downwards  as  the  load  is  applied  in  an  upward 
direction.  The  load  is  applied  through  a  knife-edge  at  the 
centre  of  the  specimen,  and  is  produced  by  sliding  the  jockey- 
weight  along  a  graduated  lever.  The  lever  itself  is  counter- 
poised, as  in  the  case  of  other  testing  machines,  so  that  it 
is  only  the  sliding  weight  which  loads  the  test  bar.  As  the 
specimen  bends,  the  lever  is  prevented  from  assuming  an 
inclined  position  by  means  of  a  screw  and  hand-wheel,  which 
take  up  the  movement  of  the  bar.  In  making  these  tests  it  is 
obvious  that  the  bars  must  be  accurately  placed  and  the  load 
applied  centrally. 

Keep's  Testing  Machine. — This  is  used  to  test  small  bars 
about  J  inch  in  thickness,  and  from  the  tests  so  made  the 
quality  of  cast-iron  is  determined.  It  is  constructed  to  trace 
a  diagram  of  the  behaviour  of  the  bar  while  under  test.  The 
load  is  applied  in  a  similar  manner  to  the  Bailey  machine,  but 
the  lever  is  not  kept  floating,  being  allowed  to  go  down  with  the 
bending  of  the  bar.  A  pencil  arm  is  attached  to  the  centre 
of  the  bar  and  a  sheet  of  paper  placed  in  the  holder  behind 
it.  The  movement  of  the  bar  is  magnified  five  times,  so  that 
the  actual  deflection  is  more  easily  measured.  The  paper 
holder  is  moved  in  a  horizontal  position  as  the  jockey  weight 
moves  along  the  lever,  the  two  being  connected  together  by 
means  of  cords.  In  this  way  a  curve  of  deflection  against 
load  is  obtained  for  each  specimen,  and  the  behaviour  of  the 
bar  under  transverse  loading  is  thus  automatically  recorded. 

The  Deflection  of  Beams. — The  apparatus  shown  in  Fig.  14 
is  for  the  purpose  of  directly  measuring  the  deflection  of  small 
beams  under  a  given  loading.  The  frame  A  carries  two  knife- 
edges  B  B,  whose  distance  apart  is  adjustable  to  suit  beams  of 
different  lengths.  These  knife-edges  support  the  beam  C 
which  is  to  be  tested  by  applying  a  load  D  through  a  knife- 
edge  at  G.  The  beam  also  carries  at  this  point  a  frame  and 
cross-wire  E,  the  position  of  which  can  be  observed  with  great 
accuracy  by  means  of  a  telescope  F.  The  load  is  applied  by 


42 


A  HANDBOOK  OF  TESTING  MATEEIALS 


To  Man 
drive 


adding  weights  at  D,  and  the  deflection  for  each  load  observed 
by  noting  the  movement  of  the  cross-wire  at  E  against  a 
suitably  graduated  scale.  In  this  way  the  accuracy  of  the 
laws  for  theoretically  determining  the  deflection  of  a  beam 
can  be  experimentally  checked  by  means  of  the  very  simple 
apparatus  just  .described.  In  some  cases  the  cross-wire  is 
placed  inside  the  telescope,  and  a  scale  graduated  to  TJo  of  an 
inch  is  fixed  vertically  to  the  centre  of  the  beam,  a  reading 
being  taken  after  the  application  of  each  load.  The  beam  may 
also  be  fixed  as  a  cantilever  by  bringing  the  two  knife-edges 

closely  together  and 
-TO  poise  actuat/ng gear  rigidly  gripping  the  end 
of  the  beam  between 
them.  An  old  lathe  bed 
can  be  used  for  the  frame- 
work of  the  apparatus. 

Automatic  Testing 
Machines. — The  general 
principle  underlying 
machines  fitted  with 
some  appliance  for  auto- 
matically keeping  the 
poise  balanced  is  as 
follows  : — 

The  load  is  applied  at 

a  constant  rate  in  the  case  of  screw  machines,  such  as  the 
Kiehle,  by  driving  the  screws  at  a  constant  speed,  or  in  the 
case  of  hydraulic  machines,  such  as  the  Wicksteed,  by 
applying  pressure  at  a  constant  rate  to  the  hydraulic 
cylinder. 

The  poise  weight  is  likewise  run  along  the  beam  at  a  speed 
which  is  adjusted  to  such  a  value  as  to  tend  to  run  out  at  a 
slightly  faster  rate  than  is  necessary  to  keep  the  machine 
balanced.  At  some  point  in  the  driving  mechanism  of  this 
latter  arrangement  is  an  electric  clutch,  which  is  put  in  or 
out  of  gear  according  as  a  contact  worked  by  the  movement 
of  the  poise  arm  is  made  or  broken. 


FIG.    15. — Change   Speed  Mechanism  in 
Poise  Gear  of  Eiehld  Testing  Machine. 


MACHINES  FOE  TENSION,   COMPEESSION,  ETC.          43 

Thus,  in  the  arrangement  sometimes  fitted  to  the  Riehle 
machines,  an  electric  contact  is  arranged  so  that  when  the 
beam  rises  it  makes  contact,  actuates  the  clutch,  and  drives 
the  weight  along  the  beam  until  balance  is  restored,  when 
the  circuit  is  broken  and  the  poise  weight  remains  stationary 
until  the  increase  in  the  load  again  raises  the  beam  and 
starts  the  poise  driving-gear  again.  This  latter  mechanism  is 
driven  by  the  same  source  of  power  as  that  which  drives  the 
screw  gear  for  applying  the  load.  The  relative  speed  of  the 
load-applying  gear  and  the  poise-controlling  mechanism  can 
be  varied  by  means  of  the  three-disc  mechanism  shown  in 
Fig.  15.  The  disc  B  is  driven  at  constant  speed,  while  the 
disc  A  can  be  moved  by  hand  along  its  shaft  and  thus  vary 
the  relative  speed  of  A  and  B.  It  is  desirable  to  adjust 
this  velocity  so  as  to  keep  the  arm  balanced  as  near  as 
possible,  independent  of  the  electric  control,  as  otherwise  the 
contact  makes  and  breaks  in  rapid  succession,  and  as  the 
circuit  is  of  necessity  highly  inductive,  violent  arcing  takes 
place,  especially  if  the  current  is  supplied  from  the  lighting 
mains  through  a  suitable  resistance,  as  is  sometimes  done. 
In  any  case,  a  certain  amount  of  trouble  is  generally  expe- 
rienced from  this  latter  cause,  and  some  skill  is  required  in 
order  to  reduce  it  as  much  as  possible. 

It  will  be  observed  that  the  mechanism  shown  in  Fig.  15 
is  reversible,  and  consequently  as  soon  as  the  maximum 
load  is  reached  it  is  desirable  to  put  this  over  to  a 
fairly  high  speed  of  reverse  and  actuate  the  clutch 
mechanism  by  hand.  No  doubt  even  this  latter  could 
be  controlled  electrically  by  placing  a  contact  on  the 
bottom  stop  and  changing  over  from  one  stop  to  the  other 
at  the  same  time  as  the  mechanism  of  Fig.  15  is  reversed, 
but  such  is  not  usually  done,  and  the  time  between 
maximum  load  and  breaking  load  is  usually  very  short, 
and  an  experienced  operator  generally  prefers  to  control  this 
portion  himself. 

A  very  fine  example  of  an  automatic  testing  machine  is 
that  installed  in  the  Northampton  Polytechnic  Institute,  built 


44  A  HANDBOOK  OF  TESTING  MATEEIALS 

by  Messrs.  J.  Buckton  &  Co.,  of  Leeds,  to  the  requirements  of 
Mr.  C.  E.  Larard.1 

In  this  machine  the  poise  weight  is  driven  by  a  separate 
electric  motor,  the  speed  of  which  can  be  varied  over  a  wide 
range  by  an  adjustable  field  resistance.  The  motor  drives 
the  poise  through  an  electric  clutch,  but  differs  from  the 
Riehle  control,  inasmuch  as  the  fall  of  the  beam  does  not 
break  the  circuit,  but  short  circuits  the  clutch  coils,  an 
arrangement  which  prevents  a  great  deal  of  the  destructive 
arcing  previously  mentioned.  A  novel  and  important  addition 
is  likewise  made  by  which  the  instant  the  clutch  is  short 
circuited  a  brake  is  applied  to  the  driving  shaft,  thereby 
preventing  any  over-running  of  the  poise  weight.  This  clutch 
is  held  off  by  means  of  an  electro-magnet,  which  is  released 
simultaneously  with  the  clutch.  The  straining  motion  is 
applied  by  hydraulic  power  from  an  accumulator,  and  the 
speed  can  consequently  be  adjusted  to  a  nicety  by  the  control 
valve.  It  is  stated  that  in  practice  it  is  found  that  the  speed 
of  straining  and  working  the  poise  weight  can  be  so  relatively 
adjusted  as  to  be  almost  independent  of  the  electric  control. 

An  important  addition  to  this  particular  machine  is  the 
provision  whereby  the  poise  weight  can  be  made  either  1,000 
or  2,000  Ibs.,  and  a  further  load  can  be  added  at  the  end  of 
the  beam,  increasing  the  maximum  load  to  150,000  Ibs., 
while  another  special  attachment  enables  torsion  loads  of 
400,000  inch-lbs.  twisting  moment  to  be  carried  out  on  short 
specimens. 

Shackles. — The  design  of  the  grips  for  holding  the  specimen 
in  the  testing  machine  is  a  very  important  point.  They  should 
be  designed  to  give  as  nearly  as  possible  a  perfectly  axial 
stress.  If  the  pull  is  not  central,  bending  of  the  specimen 
will  result,  and  the  strength  obtained  by  experiment  will  not 
be  the  true  tensile  or  compressive  strength  of  the  material. 
The  wedge  principle  is  mostly  employed  for  tension  shackles, 
to  prevent  the  specimen  from  slipping  when  the  load  is  applied. 

1  See  paper  in  Proc.  Inst.  Mech.  Eng..  July.  1!M)7. 


MACHINES  FOR  TENSION,   COMPEESSION,   ETC.          4o 


46 


A  HANDBOOK  OF  TESTING  MATERIALS 


The  principle  of  these  is  exemplified  by  the  "  Wicksteed  " 
grips,  shown  in  Fig.  16.  The  flat  test  bar  is  gripped  between 
two  wedge  grips  which  have  serrated  faces,  like  a  file,  to  pre- 
vent the  specimen  from  slipping.  The  grips  themselves  rest 
in  a  seating,  whose  inner  sides  are  inclined  to  the  same  angle 
as  the  outer  sides  of  the  wedge.  The  whole  is  secured  in  a 

round  cast-iron  plate,  which  is  fixed 
by  tension  bars  to  the  beam  on 
which  the  jockey  weight  slides.  It 
will  readily  be  seen  that,  the  greater 
the  pull  on  the  specimen,  the  more 
firmly  will  the  grips  wedge  them- 
selves in  the  seating,  and  the  more 
tightly  will  they  hold  the  specimen. 
Another  type  of  specimen  is  enlarged 
to  form  an  eye  at  each  end.  Pins 
are  passed  through  the  hole  at  each 
end  to  secure  it  to  the  forked 
shackle.  In  this  way  the  test  piece 
is  free  to  move  in  one  plane  to 
ensure  axial  loading.  The  method 
most  often  used,  however,  enables 
the  test  bar  to  move  in  any  direc- 
tion, so  that  bending  the  bar  is 
almost  an  impossibility.  This 


3L  17.— Ball  Seating  for 
Tension  Specimens  with 
Screwed  Ends. 


spherical  or  ball  ends. 


seat.  If  the  bar  is  merely  cast  and 
not  machined,  it  may  be  made  with 
The  grips,  which  are  each  made  in 
two  parts,  have  spherical  seatings  on  them,  between  which 
the  ball  ends  of  the  specimen  rest.  As  the  load  is  applied, 
these  seatings  allow  the  test  bar  to  adjust  itself  with  its  axis 
in  the  direction  of  the  pull.  When  the  specimen  is  machined, 
the  ends  are  usually  enlarged,  the  inside  end  of  the  enlarged 
part  being  spherical  in  shape,  so  that  it  is  self-adjusting  in 
the  clips ;  or  the  ends  of  the  specimen  can  be  screwed  and 
fitted  in  hemispherical  seats  as  shown  in  Fig.  17. 


MACHINES  FOE  TENSION,  COMPRESSION,  ETC.          47 


Compression  Shackles  are  easier  to  design,  merely  consist- 
ing in  most  cases  of  two  flat  parallel  plates  between  which 
the  accurately  faced  ends  of  the  cylindrical  test  piece  are 
gripped  as  the  load  comes  on.  In  some  cases,  especially 
where  long  specimens  are  used,  one  of 
these  plates  is  formed  with  a  spherical 
back,  which  adjusts  itself  in  parallel 
with  the  other. 

Where  great  accuracy  is  required,  as 
in  research  work,  it  is  necessary  to  use 
seatings  which  shall  ensure,  as  far  as 
possible,  central  loading.  Figs.  18  and 
19  show  two  methods  of  loading  ordinary 
compression  specimens.  The  method 
shown  in  Fig.  20  has  been  tried  by  the 
author,  and  found  entirely  unsuccessful. 
Fig.  21  illustrates  the  method  employed 
by  Prof.  Lilley  in  loading  hollow  struts 
during  some  of  his  classic  experiments, 
mention  of  which  will  be  found  in  the 
bibliography. 

Calibration  of  Vertical  Machines  of 
the  Wicksteed  Type.— Machines  of  this 
type  can  be  readily  tested  for  accuracy 
in  the  following  manner.  To  test  for 
wear  of  knife-edge  and  to  estimate  width 
of  edge : — 

(1)  Open  out  the  shackle  heads  to  the 
maximum    distance   apart   as    if    for    a 
compression  test. 

(2)  Carefully    ascertain    if   any   parts 

of  the  shackles  which  move  relatively  to  one  another  are  in 
contact,  as  the  friction  produced  by  this  means  may  be 
considerable. 

(3)  When  everything  is  free,  set  the  beam  indicator  so  as  to 
be   right  over   one   side  of  the  slot,  and  then  get  beam  in 
equilibrium  with  the  beam  end  near  the  top  stop. 


Alft 


FIG.  18.— Ball  Seating 
for  Specimen  in 
Compression. 


48 


A  HANDBOOK  OF  TESTING  MATEEIALS 


FIG.  19.— Method  of 
Loading  Compres- 
sion Specimen. 


Y///////////////// ///////// 

FIG.  20.— Unsuccessful  Method 
of  Loading  Compression 
Specimen. 


Sectional   Elevation. 


Plan. 


FIG.  21.— Prof.  Lilley's  Method  of  Testing  Hollow  Struts. 


MACHINES  FOE  TENSION,   COMPEESSION,  ETC.          49 

(4)  When  all  is  balanced  set  vernier  accurately  to  zero,  and 
again  adjust  for  equilibrium  if  necessary. 

(5)  Add  weights  to  the  lower  shackle  up  to  half  a  ton  or 
more.     In  this  connection  it  will  be  found  convenient  to  first 
put  on  the  cross-beam  used  in  beam  tests,  as   in   a   50-ton 
Wicksteed,  this  weighs  over  400  Ibs.,  besides  making  a  con- 
venient support  for  the  other  weights. 

(6)  Again  restore  equilibrium  and  note  reading  on  scale. 

(7)  Shift  the  beam  indicator  over  to  other  end  of  slot,  set 


FIG.  22. — Diagram  showing  Effect  of  Wear  of  Knife-Edge  in  Machines 
of  the  Wicksteed  Type. 

for    equilibrium  with   beam   nearly   on   bottom   stop;   note 
reading. 

(8)  Eemove  load ;  adjust  to  equilibrium  ;  note  reading. 

It  will  be  seen  that  we  thus  obtain — 

(a)  True  load  on  shackle. 

(b)  Eeading  of  machine  with  beam  up. 

(c)  Eeading  of  machine  with  beam  down. 
Record  of  Calibration  Test. — In  a  certain  test  on  a  50-ton 

Wicksteed  machine  the  following  results  were  obtained  :— 
(a)  1485-6   Ibs.  =  '663  tons ;  (6)  '657   tons ;   (c)  '660  tons. 

The  mean  of  (b)  and  (c)  =  '6585. 

T.M.  E 


50  A  HANDBOOK  OF  TESTING  MATEKIALS 


Hence  percentage  error  at  low  loads  =  — — —  X 100 


low. 

The  percentage  error  would  probably  be  much  less  at  higher 
load. 

The  difference  in  reading  with  the  beam  up  and  the  beam 
down  is  due  to  the  width  of  the  knife-edge. 

The  correct  distance  of  the  knife-edge  D  from  the  fulcrum 
is  3  inches,  hence  the  width  CB  is  of  the  nature 

•660- -657       ,,_^K)3        „  _ 

•6685  --6685X  3' 

Exaggerating  the  width  as  in  Fig  22,  we  see  that  when  the 

AC 
beam  is  up  the  leverage  is  ^,  and  when  the  beam  is  down 

AB' 

the  leverage  is  :™r- 


This  is  as  small  as  can  be  reasonably  be  expected. 
To  Check  the  Weight  of  the  Balance-weight.— 

(a)  Hang  some  known  weight,  say  56  Ibs.,  on  the  longi- 
tudinal scale  near  the  end  of  the  beam. 

(b)  Balance  the  machine  and  adjust  vernier  to  zero. 

(c)  Move  the  weight   through  a  definite  number   of   scale 
divisions  (preferable  40)  and  again  balance  the  machine. 

(d)  Note  how  far  the  balance-weight  has  been  moved. 

In  a  certain  test  on  the  same  machine  as  above  when  the 
56-lbs.  weight  was  moved  through  40  divisions  (from  50  tons 
to  10  tons)  the  balance- weight  was  moved  as  near  1  division  as 
could  be  read  on  the  machine.  Since  moving  56  Ibs.  through 
40  divisions  is  equivalent  to  moving  1  ton  through  1  division, 
the  balance-weight  was  certainly  within  *1  per  cent  of  1  ton. 


CHAPTEK   IV 

STRAIN-MEASURING    INSTRUMENTS 

WHENEVER  a  body  is  subjected  to  a  load,  or  stress  of  any 
kind,  some  strain  or  deformation  of  shape  is  sure  to  result. 
If  this  strain  occurs  in  finished  structures,  it  may  have  incon- 
venient or  even  dangerous  results,  so  that  we  desire  to  know 
the  actual  effect  produced  by  stressing  a  material  to  a  certain 
degree  in  changing  its  shape.  Moreover;  if  we  can  find  out 
the  separate  effect  of  each  increment  of  load,  the  stress  strain 
curve  drawn  from  such  readings  may  give  us  some  useful 
information  about  the  material  that  we  propose  to  use.  The 
most  usual  case  is  that  of  tension.  Let  us  assume,  then,  that 
we  are  about  to  test  a  bar  of  the  material  in  question,  with  a 
tensile  load  between  certain  limits.  The  immediate  effect  of 
the  application  of  this  load  will  be  to  stretch  the  bar  by  an 
amount  which  varies  with  the  intensity  of  the  load.  We  wish  to 
measure  the  amount  of  this  stretching,  which  is,  after  all,  very 
small  in  proportion  to  the  length  of  the  bar.  The  easiest  way, 
of  course,  is  to  centre-punch  the  bar  at  a  point  near  each  end, 
and  measure  the  distance  between  them  with  a  pair  of  dividers 
after  the  application  of  each  increment  in  the  load.  Another 
method  would  be  to  screw  two  collars  to  the  test  bar,  at  a 
distance  apart,  fixed  by  the  length  of  a  standard  rod.  As  the 
bar  began  to  stretch,  a  wedge  gauge  could  be  introduced  into 
the  space  between  the  end  of  the  standard  rod  and  the  bottom 
collar,  the  extension  thus  being  measured  with  very  fair  accuracy. 
But  these  methods  are  quite  inadequate  to  measure  the  very 
small  extensions  which  take  place  at  stresses  below  the  elastic 
limit  of  the  specimen.  These  it  is  most  valuable  for  us  o 
know,  as  it  is  only  at  stresses  below  the  elastic  limit  that  any 
material  can  be  used.  For  the  purpose  of  measuring  these 

E  2 


52  A  HANDBOOK  OF  TESTING  MATEEIALS 

minute  extensions,  some  form  of  "  extensometer  "  must  be 
used.  In  these  instruments  the  stretching  of  the  specimen  is 
magnified  either  by  mechanical  or  optical  means,  until  the 
slightest  extension  can  be  measured  with  an  accuracy  ranging 
from  JODOO  °f  an  incn  ^n  ^ne  former  case  to  jooiooo  °^  an 
inch  in  some  forms  of  optical  instruments. 


Screw 


f*\  icrom  cKc,t\ 


FiG.^23.— Ewing's  Extensometer. 

E  wing's  Extensometer. — A  diagram  of  this  instrument  is 
shown  in  Fig.  23.  The  framework  of  this  extensometer,  which 
is  indicated  by  thick  black  lines  in  the  diagram,  is  secured  to 
the  specimen  by  screws  at  A  and  B.  The  distance  between 
them,  generally  called  the  gauge  length,  is  usually  eight  inches. 
As  the  test  bar  stretches,  the  distance  A  B  becomes  greater,  and 


STRAIN-MEASURING  INSTRUMENTS 


as  the  end  H  is  fixed  in  position  relative  to  the  frame,  it  will 
readily  be  seen  that  the  movement  of  G  will  be  double  that  of 
B.  The  movement  of  G  is  observed  by  the  passage  of  a  cross 
hair  C  along  a  graduated  scale  in  the  eye-piece  of  the  telescope 
D,  which  is  capable  of  adjustment  by  means  of  the  screw  E. 


&%>. — 


.  c^afl 


0 


i 


Cross  Wire 


Microscope 


FIG.  24. — Diagrammatic  Outline  of  Latest  Type  Ewing's  Extensometer. 

The  graduated  scale  is  calibrated  by  means  of  the  micrometer 
screw  F,  which  is  turned  through  a  known  distance,  and  the 
movement  of  C  observed.  The  actual  value  of  each  scale 
division  can  thus  be  obtained  in  a  very  simple  manner,  the 
accuracy  being  about  ^oioo  °^  an  inch. 

In  the  latest  type  of  this  important  instrument  some 
modifications  have  been  made  in  the  general  arrangement, 
although  not  in  the  principle.  Fig.  24  shows  this  latest  form. 


54  A  HANDBOOK  OF  TESTING  MATERIALS 

The  object  sighted  is  one  side  of  a  wire  stretched  hori- 
zontally across  a  hole  in  the  bar  K  and  illuminated  by  a 
small  mirror  behind.  The  distances  C  P  and  C  Q  are  in  this 
instance  equal,  with  the  effect  that  the  movement  of  the  sighted 
mark  is  double  the  extension  of  the  rod.  The  length  of  the 
microscope  is  adjusted  so  that  one  turn  of  the  screw  causes  the 
mark  to  pass  over  50  scale  divisions  in  the  eye-piece.  This 
adjustment  should  be  tested  with  an  extensometer  as  mounted 
on  the  specimen,  and,  if  need  be,  the  length  of  the  microscope 
tube  can  be  altered  by  drawing  out  or  in  the  portion  carrying 
the  eye-piece.  A  complete  revolution  of  the  screw  L,  which 
has  a  pitch  of  /^th  of  an  inch,  should  cause  a  displacement 
of  the  mark  through  50  divisions  of  the  eye -piece  scale. 
Eeadings  are  taken  to  tenths  of  a  scale  division,  so  that  this 
displacement  corresponds  to  500  units.  Each  unit  then 
means  g^ou  inch,  in  the  extension  of  a  test-piece. 

The  scale  engraved  in  the  eye -piece  of  the  microscope  has 
140  divisions  each  corresponding  to  ^V^  inch  of  extension, 
and  by  estimation  of  tenths  of  a  division  readings  are  taken 
to  -soiioo  inch. 

The  screw  L  further  serves  to  bring  the  sighted  mark  to  a 
convenient  point  on  the  micrometer  scale,  and  also  to  bring 
the  mark  back  if  the  strain  is  so  large  as  to  carry  it  out  of 
the  field  of  view ;  thus,  a  single  turn  of  the  screw  adds  500 
units  to  the  range  shown  on  the  micrometer  scale.  In  dealing 
with  elastic  strains  there  is  no  need  for  this,  as  the  range  of  the 
scale  is  itself  sufficient  to  include  them,  but  it  is  useful  when 
observations  are  being  made  on  the  behaviour  of  metals  as 
the  elastic  limit  is  passed. 

In  other  forms  of  this  instrument  the  micrometer  is  dispensed 
with,  the  position  of  the  telescope  relative  to  the  frame  being 
fixed.  The  scale  in  the  eye-piece  of  the  telescope  is  then  so 
graduated  that  its  divisions  represent  some  definite  fraction 
of  an  inch. 

Unwin's  Extensometer.  —  In  Prof.  Unwin's  instrument, 
shown  in  Fig.  25,  two  tee-brackets  are  fixed  to  the  specimen 
a  gauge  length  apart.  To  each  of  these  brackets  a  spirit  level 


STRAIN-MEASURING  INSTRUMENTS 


55 


is  attached,  so  that  they  can  always  be  kept  exactly  in  a 
horizontal  position.  To  the  lower  bracket,  in  addition,  is 
clamped  the  measuring  pillar  C,  which  carries  within  it  a 
fine  screw  D,  with  a  micrometer  head  E.  This  screw  has 


FIG.  25. — Un win's  Extensometer. 

50  threads   per   inch,    and,    since   the   micrometer   has   200 
divisions,  an  accuracy  of  joioo  °f  an  incn  *s  obtainable. 

When  about  to  take  a  reading  the  lower  bracket  is  first 
levelled  by  the  adjusting  screw  F,  and  then  the  upper  bracket 
is  levelled  by  the  micrometer.  The  difference  between  this 
micrometer  reading  and  the  previous  one  gives  us  the  caange 
in  length  of  the  specimen. 


56 


A  HANDBOOK  OF  TESTING  MATERIALS 


Marten's  Extensometer. — Fig.  26  is  a  diagrammatic  sketch 
of  Marten's  instrument.  An  arm  A  with  a  point  at  its  lower 
end  is  clamped  to  the  specimen  by  elastic  bands  or  springs  at 
B  and  C.  Between  the  top  end  and  the  specimen  there  is  a 


r  - 


EiG.  26. — Marten's  Pointer 
Extensometer. 


FIG.  27. — Ashcroft's 
Extensometer. 


small  diamond-shaped  lever  E.  Any  movement  of  A  relative 
to  the  specimen,  such  as  is  caused  by  an  extension,  tilts  the 
piece  E,  thus  moving  a  long  pointer  D  over  a  fixed  scale  F. 
When  the  magnification  is  50,  readings  can  be  conveniently 
taken  to  ^ Jn  mm. 

Ashcroft's   Extensometer. — An    instrument    described   by 
Ashcroft  is  shown  in  Fig.  27. 


STRAIN-MEASURING  INSTRUMENTS 


57 


The  upper  end  of  the  knife-edge  B  is  rigidly  connected  to 
the  upper  end  of  the  specimen  whilst  A  is  clamped  to  the 
lower.  A  and  B  fit  into  small  notches  in  the  lever  D,  and 
consequently  a  greatly  magnified  movement  of  the  relative 


FIG.  28. — Kennedy's  Exteusometer. 

motion  of  A  and  B  is  shown  by  a  pointer  D  on  a  fixed 
scale  C. 

Kennedy's  Extensometer. — This  is  almost  identical  in 
principle  with  that  of  Martens.  Fig.  28  shows  the  instru- 
ment in  outline,  and  is  practically  self-explanatory.  Beading 
can  be  taken  to  the  nearest  TUJoo  or  20000  incn- 

Stromeyer's  Rolling  Pin  Type  Strain  Indicator. — This  type 


58 


A  HANDBOOK  OF  TESTING  MATERIALS 


of  instrument  is  shown  diagrammatically  in  Fig.  29  adapted 
for  the  measurement  of  strains  in  testing-machine  specimens. 
A  modified  form,  but  involving  the  same  principle,  has  been 
largely  used  for  the  measurement  of  strains  in  finished 
structures  such  as  bridges. 

It  will  be  seen  that  in  the  instrument  illustrated  in  Fig.  29 
two  flat  strips  A  B  and  C  D  are  held  together  by  springs  E 
and  F.  Between  them  is  a  small  roller  G  consisting  of  a 
piece  of  circular  wire  which  has  been  carefully  prepared  so 
as  to  be  as  nearly  an  exact  circular  section  as  is  possible. 


FIG.  29. — Stromeyer's  Boiling  Pin  Extensometer. 

The  ends  C  and  B  are  clamped  to  two  points  of  the 
specimen  which  move  relatively  when  the  specimen  extends. 
The  motion  of  A  B  over  C  D  causes  the  roller  G  to  turn, 
which  movement  is  read  by  observing  the  movement  of  a 
pointer  H  over  a  fixed  scale  J.  Kesults  have  been  obtained 
in  which  each  scale  division  represents  joioo  inch,  and  a 
further  estimation  could  be  made.  In  the  design  of  instrument 
used  on  existing  structures,  shown  in  Fig.  30,  A  is  the  roller 
moving  between  a  fixed  plate  C  and  a  moving  one  B. 

B  is  connected  to  the  upper  gauge  clamp  by  a  piece  of 
annealed  wire  F  of  the  same  material  as  the  structure.  F  is 
kept  tight  by  means  of  a  spring  E.  The  gauge  length  is 


STRAIN-MEASURING  INSTRUMENTS 


between  the  screws  H  H  and  G  G.     The  rolling  pins  are 

made  of  hardened  cast-steel. 

They  are  attached  to  light 

straw  pointers  by  means  of 

paper  envelopes  and  sealing 

wax.      The   papers  are   cut 

after    fixing,    so    that    the 

pointer  is  balanced.     These 

rolling     pin     pointers     can 

easily  be  renewed  or  re-fixed 

with     a     warmed     pair    of 

pincers,  and  this  is  generally 

necessary      when       sudden 

strains,    which    appear    to 

act  like  blows,  are  recorded 

by    the     instruments.      In 

such      cases       the      straw 

pointers  will  generally  break 

off.      It    is    not     advisable 

to    replace    them    by    wire 

pointers,  for  then  even  small 

but   sudden  strains  have  a 

powerful   effect   and   loosen 

the  rolling  pin,  which  defect 

is  not  always  noticeable  and 

may  lead  to  errors. 

The  Cambridge  Extenso- 
meter.  —  This  instrument, 
the  general  scheme  of  which 
is  shown  in  Fig.  31,  consists 
of  two  separate  parts,  each 
of  which  is  separately 
attached  to  the  test-piece  A 
by  hard  conical  points. 

The  steel  rods  carrying  these  points  slide  in  geometric  slides, 
and  after  being  driven  gently  in  centre  punch  marks  at  P  and  P l 
are  clamped  in  position.  Both  parts  of  the  instrument  should 


FIG.  30.  —  Stromeyer's  Rolling  Pin 
Type  Extensometer  (as  used  on 
finished  structures). 


60 


A  HANDBOOK  OF  TESTING  MATERIALS 


be  capable  of  rotating  quite  freely  about  the  points,  but  there 
must  be  no  backlash.  The  lower  piece  carries  a  micrometer 
screw  fitted  with  a  hardened  steel  point  B,  and  a  divided 
head  C.  It  also  carries  a  vertical  arm  D,  at  the  top  of  which 
is  a  hardened  steel  knife-edge.  The  upper  and  lower  pieces 
work  together  about  this  knife-edge,  the  balance  weight 
serving  to  keep  the  two  parts  in  contact.  A  nickel-plated 


Balance  Weight 


Graduated  Scale^ 


FIG.  31. — Cambridge  Extensometer. 

flexible  steel  tongue  F,  forming  a  continuation  of  the  upper 
piece,  is  carried  over  the  micrometer  point  B.  This  tongue 
acts  as  a  lever,  magnifying  the  extension  of  the  specimen, 
so  that  the  movement  of  the  steel  tongue  to  or  away  from 
the  point  B  is  five  times  the  actual  extension  of  the  specimen. 
To  take  a  reading  the  thin  steel  tongue  F  is  caused  to  vibrate, 
and  the  divided  head  then  turned  till  the  point  B  just  touches 
the  hard  steel  knife-edge  on  the  tongue  as  it  vibrates  to  and 
fro.  This  has  proved  to  be  the  most  delicate  method  of 
setting  the  micrometer  screw,  as  the  noise  produced  and  the 


62  A  HANDBOOK  OF  TESTING  MATERIALS 

fact  that  the  vibrations  are  quickly  damped  out  indicate 
to  jouo  mm-  ^ne  instant  when  the  screw  is  touching  the 
tongue.  This  instrument  is,  according  to  the  National 
Physical  Laboratory's  report,  reliable  to  about  one-thousandth 
part  of  a  millimetre. 

Optical  Instruments. — Greater  sensitiveness  than  that 
given  by  any  of  the  foregoing  instruments  can  in  general  only 
be  attained  by  some  optical  appliance.  There  has  been  rather 
a  prejudice  against  the  use  of  optical  instruments  in  this 
country,  probably  on  account  of  difficulties  in  focussing,  etc. 
This  is,  however,  less  noticeable  now  than  formerly.  These 
optical  instruments  were  first  used  on  the  Continent.  Their 


dh 

FIG.  33.— Marten's  Mirror  Extensometer. 

great  advantage  is  the  employment  of  a  weightless  lever — a 
beam  of  light — for  magnification  purposes. 

Bauschinger's  Apparatus.— Fig.  32  shows  an  instrument 
designed  by  Bauschinger.  a  a  and  b  b  are  the  points  held  in 
by  suitable  clips  to  the  gauge  points  of  the  specimen.  The 
connection  between  the  two  parts  of  the  instrument,  one  of 
which  is  fixed  at  a  and  the  other  at  6,  is  a  rolling  one  formed  by 
a  caoutchouc  roller  c  moving  over  a  light  spring  d.  Hence,  as 
the  two  gauge  points  move  relative  to  one  another,  the  roller  c 
is  turned  in  a  similar  manner  to  that  in  Stromeyer's instrument. 
The  twisting  of  the  roller  moves  a  small  mirror  e,  the  angle  of 
movement  being  observed  by  means  of  a  telescope  at/.  Readings 
can  be  taken  to  TQ  Juo  mm-  It  will  be  observed  that  readings 
are  taken  on  both  sides,  and  to  Bauschinger  belongs  the  credit 
of  first  realising  the  necessity  of  measuring  strains  in  more 
than  one  plane,  an  idea  which  has  since  been  extended  by  the 
author  to  three  planes  at  120°  apart. 


STKAIN-MEASUBING  INSTRUMENTS 


0 


Marten's  Mirror  Extensometer. — In  another  form  of  optical 
instrument  devised  by  Martens,  the  rollers  used  by  Bauschinger 
are  replaced  by  small  diamond-shaped  knife-edges.  Figs.  33 
and  34  illustrate  this  instrument.  Like  Bauschinger's  instru- 
ment, it  measures  strains  on  two  sides.  A  A  are  two  flat 
plates  having  knife-edges  at  E.  They  are  held  together  by 
springs  B  on  each  side,  and  press  on  knife-edges  at  C.  Fig.  34 
shows  another  view  of  the 
diamond  pieces,  and  the 
method  of  carrying  the 
mirrors.  M  is  the  mirror 
pivoted  in  the  frame  P 
by  small  set  screws  at 
N  N.  On  the  other  side 
a  set  screw  presses  against 
the  mirror,  whose  motion 
is  resisted  by  a  small 
spring  D.  This  allows 
the  inclination  of  the 
mirror  to  be  adjusted. 
E  is  a  weight  to  balance 
the  mirror,  and  T  a 
pointer  which,  when  set 

in  contact  with  the  bar  S,  indicates  that  the  knife-edge  Q  is 
correctly  at  right  angles  with  the  bar  S. 

Morrow's  Extensometer.  —  Yet  another  form  of  optical 
instrument  is  one  devised  by  Dr.  Morrow,  which  embodies 
the  same  principle  as  Marten's  but  is  so  arranged  that  the 
image  of  a  scale  held  some  distance  away  can  be  viewed  in 
the  mirror  by  means  of  a  telescope.  A  second  stationary 
mirror  reflects  the  zero  mark.  This  instrument  is  said  to 
read  to  j^oJooo  °f  an  inch,  having  a  magnification  of  about 
3,000. 

Stromeyer's  Optical  Extensometer. — An  extensometer  of 
great  delicacy  was  designed  by  Mr.  C.  E.  Stromeyer  in  the 
eighties,  originally  for  the  measurement  of  local  strains  in 
metal  structures,  but  the  particular  design  illustrated  was 


r.        1    i        r 

^p 

^D 
N                  N 
M 

{ 

FIG.  34.— Detail  of  Mirror  Attachment, 
Marten's  Extensometer. 


A  HANDBOOK  OF  TESTING  MATERIALS 


specially  designed  for  measuring  the  cross  contraction  of  test 
pieces  in  order  to  obtain  a  direct  measurement  of  Poisson's 

Batio.1  It  depends 
on  the  important 
principle  of  the  in- 
terference of  light. 
If  white  light  is 
projected  on  to  a 
small  piece  of  dark 
glass,  the  reflected 
ray  can  be  con- 
sidered as  made  up 
of  two  parts,  one 
reflected  from  the 
outer  surface  and 
one  from  the  back 
surface.  Since  one 
has  travelled 
slightly  farther 
than  the  other,  the 
two  rays  will  not 
be  exactly  in  phase, 
the  consequence 
being  that  they 
interfere  and  in 
the  case  of  white 
light  the  reflected 
ray  would  be  split  up  into  coloured  bands,  while  in 
the  case  of  yellow  sodium  light,  which  is  used  with  this 
instrument,  alternate  bands  of  dark  and  light  are  observed 
when  the  reflected  ray  is  seen  in  a  suitable  form  of  telescope. 
If  before  being  reflected  by  the  dark  glass  the  light  suffers  a 
previous  reflection  at  another  surface  and  the  two  reflecting 
surfaces  are  moved  relative  to  one  another,  the  dark  inter- 
ference bands  will  appear  to  move  along  the  second  surface 
past  a  line  which  can  be  scratched  on  the  surface.  The 


FIG.  35.— Stromeyer's  Optical  Extensometer. 


1  See  p.  134. 


STKAIN-MEASUEING  INSTRUMENTS 


65 


Washers 
for  fasten- 
ing. 


Twisted 
Strip. 


\M  Mirror. 


distance  apart  of  the  interference  bands  can  be  calculated  and 
also  the  relative  movement  of  the  two  reflecting  surfaces  for  a 
given  movement  of  the  bands  past  the  fixed  line. 

Fig.  35  shows  a  diagrammatic  sketch  of  the  method  used  to 
carry  out  this  principle  in  practice.  T  is 
the  section  of  the  test  piece  which  is 
pressed  against  the  point  on  the  frame  F 
by  the  screw  S.  G  is  the  dark  glass  which, 
as  soon  as  T  contracts,  is  pulled  away  from 
the  glass  prism  P  by  means  of  the  four 
helical  springs1  Z  Z  which  surround  the 
columns  C  C  and  which  are  firmly  secured 
to  the  frames  F2  F3.  The  latter  carry  the 
adjustable  glass  prism  P,  which  is  so  shaped 
that  the  ray  of  sodium  light  LI  does  not 
coincide  with  its  reflected  ray  L2. 

The  source  of  light  was  a  sodium-tinted 
Bunsen  flame,  while  L2  was  observed 
through  a  telescope.  The  inclination  of 
the  rays  of  light  in  the  narrow  space 
between  the  prism  P  and  the  dark  glass  G 
was  carefully  measured,  and  found  to  be 
19°,  so  that  each  interference  band,  as  seen 
in  the  reflected  yellow  light,  ought  to 
represent  a  distance  of  "0000109  inches. 
That  is  to  say,  a  relative  movement  of  the 
two  frames  of  this  amount  would  cause  a 
movement  of  the  dark  bands  equal  to  their 
distance  apart.  Careful  measurements  with 
the  fine  screw  S,  however,  showed  the  move- 
ment to  represent  "0000120  inches,  or  10 
per  cent.  more. 

The  Sphingometer. — This  instrument  may  be  employed  to 
measure  strains  in  one,  two  or  more  planes.     Calibration  is 
made  for  each  test,  if  it  is  desired  to  note  the  elastic  con- 
stants ;  if  it  is  only  desired  to  note  the  load  at  certain  marked 
1  There  are  two  other  springs  and  columns  not  shown. 

T.M.  F 


Twisted 
strip. 


Washers 
for  fasten- 
ing. 


FIG.  36. — Strips  for 
Sphingometer. 


66 


A  HANDBOOK  OP  TESTING  MATERIALS 


points,  calibration  is  unnecessary.  The  adaptation  of  the 
instrument  for  meaburement  of  strains  in  one  or  two  planes 
will  be  fairly  obvious  if  the  type  used  for  measurement  in 
three  planes  is  described. 

The  results  obtained  by  experiment  show  that,  with  ordinary 


R  ---  Twisted,  Strip. 
M  ---  Mirror. 
K  ---  Micrometer. 


L 

U 
0 

N 


N- 


_  Sliding  bush  to  \^J 

r^? 
which  strip  is  fastened. 

_  Set  screws. 
_  Feather  key. 
-Spring. 


FIG.  37. — Section  through  Sphingometer  Strip  Holder. 

methods  of  testing,  there  is  a  considerable  variation  in  the 
stress  on  the  bar.  It  is  suggested  that  this  is  due  to  the 
fact  that  the  load  never  passes  directly  through  the  axis  of  the 
specimen.  It  is  therefore  misleading  to  divide  the  total  load 
registered  on  the  testing  machine  by  the  area  of  the  specimen 
in  order  to  estimate  the  maximum  stress  on  the  material. 


STEAIN-MEASUEING  INSTEUMENTS 


67 


To  avoid  this  error  the  author  has  devised  a  special  form  of 
extensometer  for  the  purpose  of  measuring  the  strain  on  a 
specimen,  in  tension  or  compression,  in  three  planes. 

The  general  principle  on  which  the  instrument  depends  is 
that  of  the  twisted  strip  used  by  Professors  Ayrton  and  Perry, 
who  have  shown  that  the  angular  rotation  of  a  mirror  fastened 


. 

FIG.  38. — Strip  Carrier  and  Specimen  Grip  for  Sphingometer. 

to  a  strip,  as  described  below,  is  proportional  to  the  extension 
(or  shortening)  of  the  length  oFthe  strip. 

A  piece  of  phosphor  bronze,  about  7  inches  long,  J  inch 
wide,  and  0*004  inch  thick,  is  used  (Fig.  36).  The  material  is 
divided  into  two  lengths.  At  the  centre  an  attachment  is 
made  so  that  a  mirror  (preferably  of  about  1  metre  focus)  may 
be  fastened.  One-half  of  the  strip  is  then  wound  as  a 
right-handed  spiral,  and  the  other  half  is  wound  as  a  left- 
handed  spiral.  At  the  two  ends  the  strip  is  soldered  to  a  thin 

F  2 


68  A  HANDBOOK  OF  TESTING  MATERIALS 

strip  of  metal,  which  has  drilled  through  it  a  hole  for  a  set 
screw.  By  means  of  this  set  screw  at  each  end  the  strip  is 
attached  to  a  tube  in  which  it  is  carried.  By  fastening  this 
tube  to  a  frame  with  two  set  screws,  to  secure  the  frame  to 
the  specimen,  an  extension  of  the  length  of  the  specimen 
between  the  two  fastening  screws  can  be  measured. 

During  the  author's  experiments  it  was  found  that  different 
strains  were  recorded  on  the  same  specimen  if  the  points  of 
attachment  were  moved  round  the  bar.  The  instrument  has, 
therefore,  been  arranged  to  take  measurements  in  three 
planes,  three  tubes  of  the  form  shown  in  Fig.  37  being  used, 
which  were  clamped  to  the  carrier  (Fig.  38)  by  means  of  the 
V-blocks  V.  The  carrier  grips  the  specimen  centrally  by  the 
set  screws  F,  which  are  screwed  in  so  as  to  space  the  strips 
equi-distantly  from  one  another  and  from  the  centre.  A  lamp 
is  arranged  so  that  a  ray  of  light  is  reflected  by  the  mirror  on 
to  a  scale  usually  placed  about  1  metre  from  the  mirror. 

For  calibrating  the  strip  a  known  extension  is  given  by  rotat- 
ing a  micrometer  head.  The  effect  of  this  is  that  the  beam  of 
light  passes  across,  say,  100  scale  divisions,  when  the  micro- 
meter head  shows  that  the  strip  has  been  extended,  say, 
TifW  Part  °f  an  inch.  In  which  case  each  scale  division  is 
clearly  jodooo  Par^  °f  an  inch. 

When  the  instrument  is  in  use,  T  and  T'  are  rigidly 
clamped  in  position  to  the  upper  and  lower  points  of  con- 
nection to  the  specimen.  From  the  figure  (37)  it  will  be  seen 
that  when  the  micrometer  head  K  is  turned  round,  the  bush 
L  is  forced  down,  compressing  the  spring  N  and  shortening 
the  strip  E,  E.  This  causes  the  mirror  to  rotate.  If  it  is 
desired  to  change  the  direction  of  the  beam  of  light  across 
the  scale  during  calibration,  the  micrometer  head  is  turned 
round  in  either  direction,  the  spring  N  forcing  the  bush  L 
up  when  K  is  unscrewed. 

It  will  be  seen  that  the  carriers  are  built  up  of  three 
castings,  C,  which  are  interchangeable.  They  are  screwed 
on  to  distance  pieces,  D.  By  altering  the  position  of  the 
points,  at  which  the  castings  are  fastened  to  D,  the  size  of 


STRAIN-MEASURING  INSTRUMENTS 


69 


the  triangle  can  be  altered  at  will.  This,  therefore,  gives 
the  desired  flexibility  as  regards  the  diameter  of  the  speci- 
men. Flexibility  concerning  the  length  between  the  gauge- 
points  of  the  specimen  is  secured  by  altering  the  position  of 
the  sphingometer  casing  in  the  V-blocks.  The  limiting  dis- 
tance is  the  thickness  of  one  of  the  castings  0,  which  is 
about  half  an  inch.  In  order  to  extend  the  length  between 
the  gauge-points  beyond  that  shown  in  Fig.  37,  a  longer 


i 


SCALE   DEFLECT/OMS 

FIG.  39. — Calibration  Curve  for  Sphingometer  Strip. 

tube  is  used  at  T',  and  this  can  be  extended  indefinitely.  It 
is,  therefore,  obvious  that  the  distance  between  the  gauge-points 
may  be  any  length  required  from  half  an  inch  upwards. 

Experience  has  proved  that  in  calibration  the  most  satis- 
factory method  is  to  work  across  the  scale  in  sections.  This 
removes  any  error  due  to  the  non-curvature  of  the  scale. 
It  makes  it  also  quite  a  simple  matter  to  read  direct  the 
actual  extension ;  Fig.  3(J  shows  the  method  employed.  It 


70 


A  HANDBOOK  OF  TESTING  MATEEIALS 


will  be  seen  that  the  readings  are  plotted  against  each  other 
on  squared  paper. 

The  sphingometer   is  generally   used  for  tension  or  com- 
pression tests,  but  by  the  addition  of  another  strip  and  casing, 


A..  Specimen,. 

C  .Carriers. 

D .  Sphingometer  strips . 

T  *Torslon  „     . 

M;  Micrometer  heads. 

Z  -.  Z£/Y>  mirror. 


FIG.  40. — The  Sphingometer  fitted  with  Torsion  and  Tension  Strips  (for 
description  of  Torsion  Attachment,  see  page  124). 

torsion  tests  can  also  be  carried  out  by  the  instrument. 
This  torsion  sphingometer  is  on  a  plane  perpendicular  to  the 
plane  of  the  tension  strips.  The  illumination  for  this  torsion 
mirror  is  obtained  from  the  same  lamp  as  that  used  for  the 
tension  mirrors.  In  Fig.  40  is  shown  an  isometric  projection  of 
the  instrument.  The  torsion  fitting  is  explained  fully  later. 
It  has_been  found  advantageous  to  use  gauges  in  order 


STKAIN-MEASUKINa  INSTRUMENTS  71 

to  insure  that  the  two  carriers  are  parallel.  When  the 
instrument  is,  for  the  first  time,  put  on  a  specimen,  the 
procedure  is  as  follows :  Steel  distance  pieces  are  placed 
in  the  V-blocks,  made  to  hold  the  tubes  in  which  are  carried 
the  strips.  A  gauge  is  then  inserted  at  each  corner  of  the 
carriers.  This  gauge  can,  of  course,  be  altered  for  varying 
lengths  of  specimens.  When  the  instrument  is  changed  over 
from  one  specimen  to  another  of  a  smaller  or  greater  dia- 
meter it  is  convenient  to  use  a  gauge  to  ensure  that  all 
of  the  three  fastening  screws  are  at  equal  distance  from  the 
carrier  frame.  If  it  is  desired  to  remove  the  instrument 
from  one  specimen  to  another  one  of  the  same  gauge  length, 
all  that  is  necessary  is  to  remove  the  sphingometer  tubes  and 
insert  the  steel  distance  pieces.  The  relative  positions  of 
the  carriers  cannot  then  change,  and  the  framework  is  quite 
rigid. 

One  of  the  most  important  facts  noticed  by  the  use  of  the 
instrument  is  the  variation  in  strain  which  accompanies  a 
tensile  or  compressive  stress.  Bending,  probably  due  to 
eccentric  loading,  occurs  always.  It  is  to  be  expected  that 
when  a  specimen  is  in  compression  there  will  be  bending. 
In  order,  therefore,  to  emphasise  the  importance  of  this  fact 
of  variation  of  strain  the  author  will  confine  his  remarks 
to  the  tension  tests. 

The  problem  of  axial  loading  for  a  tension  specimen  is 
more  difficult  than  would  at  first  sight  appear.  A  spherical 
seat  (Fig.  17)  may  be  used  to  secure  alignment,  but  whatever 
precautions  be  taken  to  make  the  spherical  seatings  an 
accurate  fit,  it  is  doubtful  whether  they  do  pull  into  line 
when  once  the  load  is  applied.  In  any  case,  it  has  been 
found  from  the  results  of  tests  that  more  uniform  stress 
distribution  exists  when  spherical  seats  are  used  than  when 
the  specimen  is  held  in  the  ordinary  wedge  grips. 

The  unequal  distribution  of  stress  upon  the  specimen  is 
the  most  determining  cause  of  the  unequal  strains  recorded 
during  the  experiments.  It  is  the  strain  readings  just  pre- 
vious to  elastic  failure  which  are  most  important.  From 


72  A  HANDBOOK  OF  TESTING  MATERIAL 

these  we  are  able  to  deduce  the  maximum  stress  upon  the 
material,  and  compare  it  with  the  mean  stress.  To  show 
this  clearly  the  author  may  mention  a  test,  carried  out  by 
him,  in  which  a  specimen  of  mild  steel  showed  from  such 
deductions  that  a  maximum  stress  of  more  than  13  tons  per 
square  inch  was  really  on  the  specimen,  while  the  mean 
stress  recorded  was  4'5  tons.  This  was  an  extreme  case, 
but  it  would  have  been  passed  as  normal  under  the  usual 
conditions  of  recording  extensions.  In  other  words,  it  would 
have  been  recorded  that  the  material  had  a  load  of  4*5  tons 
at  elastic  failure,  from  which  the  average  stress  is  37,980  Ibs., 
whereas  really  the  maximum  stress  was  practically  three  times 
this  amount.  The  results  of  a  test  are  given  on  p.  113. 

Autographic  Recorders. — When  a  material  is  tested  in 
tension  or  compression,  certain  strain-measuring  instruments, 
to  be  described  later,  are  of  value  for  recording  the  stretch  of 
the  specimen  under  load,  so  long  as  it  is  elastic.  There  is, 
however,  a  critical  load  at  which  the  strain  ceases  to  be  even 
approximately  proportional  to  the  stress,  and  after  this  load 
is  passed  the  instruments  useful  for  noting  stretch  during  the 
elastic  period  are  too  sensitive. 

There  are  two  methods  of  procedure  which  may  then  be 
followed  if  the  stretch,  after  the  material  is  no  longer  elastic, 
is  to  be  noted.  An  observer  may  take  certain  measurements 
of  the  distance  between  the  gauge  points,  the  load  at  the 
instant  the  reading  is  taken  being  carefully  noted.  Or  an 
arrangement  may  be  fitted  so  that  both  the  load  and  the 
stretch  are  automatically  recorded. 

It  is  usually  the  practice  to  fit  the  recorder  to  the  specimen 
before  the  test  commences.  The  scale  of  the  diagram  on 
which  the  strain  is  thus  automatically  traced  is  important. 
If,  as  is  usual,  it  does  not  exceed  ten  times  that  of  the  actual 
strain,  the  value  of  the  diagram  is  in  the  fact  that  it  gives  a 
continuous  record  of  the  relationship  of  stress  and  strain 
after  the  material  is  no  longer  elastic.  It  is  not  sufficiently 
accurate  for  obtaining  the  value  of  coefficients  within  the 
period  of  elasticity.  The  following  description  of  some 


STKAIN-MEASUKING  INSTEUMENTS  73 

ingenious  autographic  recorders  will  show  how  these  diagrams 
are  obtained. 

Unwin's  Stress-Strain  Recorder. — This  apparatus,  as  its 
name  indicates,  automatically  draws  a  stress-strain,  or  rather 
a  load-extension  diagram,  without  any  readings  being  taken 


PIG.  41. — Unwin's  Stress-Strain  Recorder. 

at  all.  This  is  done  by  using  a  rotating  drum,  as  in  the  case 
of  the  steam-engine  indicator.  It  is  necessary  to  give  the 
pencil  two  motions  at  right  angles :  one  motion  proportional 
to  the  load  put  on  the  specimen,  and  the  other  proportional  to 
the  extension  produced  by  that  load.  To  obtain  the  latter  of 
these  two  motions,  two  clamps  are  fixed  to  the  specimen,  a 
gauge  length  apart,  to  each  of  which  is  fixed  a  pulley  A  A. 
Similar  pulleys  are  fixed  at  B  and  C.  A  thin  wire-cord,  to 


A  HANDBOOK  OF  TESTING  MATERIALS 


D 

C 

u 

j£ 
u 

1 

1° 

£ 

/       r 

which  the  pencil  D  is  attached,  passes  round  these  pulleys,  in 
the  manner  shown  in  Fig.  41,  and  teminates  in  a  weight  W 


STKAIN-MEASUKING  INSTEUMENTS  75 

to  keep  all  taut.  Thus,  by  this  arrangement,  any  extension  of 
the  specimen  is  reproduced  to  double  the  scale  by  the  vertical 
movement  of  the  pencil.  Any  total  movement  of  the  specimen, 
due  to  slipping  in  the  grips,  does  not  affect  the  pencil,  as  the 
wire  between  the  specimen  and  the  drum  is  made  long 
enough  to  prevent  this. 

The  motion  proportional  to  the  load,  at  right  angles  to  the 
extension  movement,  is  obtained  by  rotating  the  drum  E, 
which  gives  essentially  the  same  result  as  moving  the  pencil 
horizontally  in  the  opposite  direction.  This  is  obtained  from 
the  shaft  which  moves  the  weight  along  the  beam,  and  so 
actuates  the  load.  As  this  shaft  rotates,  it  turns  the  pulley  G 
which  drives  the  pulley  H  by  means  of  a  wire  driving-cord  F. 
The  worm-wheel  K  is  rotated  by  means  of  a  shaft  and  worm 
from  H,  and  so  the  rotation  of  the  drum  E  is  proportional  to 
the  movement  of  H,  and  hence  to  the  load  on  the  specimen. 

Wicksteed's  Apparatus. — The  apparatus  shown  in  Fig.  42 
is  also  used  for  this  purpose.  Two  arms  A  and  B  rest  against 
projections  fastened  to  the  gauge-points.  The  arm  B  is 
supported  in  a  horizontal  position  by  means  of  levers  and 
a  balance  weight  H.  The  continuation  of  the  arm  A  is  bent 
downwards,  and  is  guided  in  a  vertical  direction  by  a  bearing 
E.  This  part  of  the  arm  is  also  provided  with  a  rack  C,  which 
gears  with  the  pinion  D.  Consequently,  when  the  specimen 
stretches,  the  arm  A  moves  relatively  to  B,  and  so  rotates  the 
pinion  D.  This  rotation  is  transmitted  through  bevel  gearing 
to  the  drum  F,  whose  motion  is  thus  proportional  to  the 
extension  of  the  test  bar. 

The  screwed  shaft  K,  which  moves  the  load  along  the 
stillion,  rotates  at  the  same  time  the  bevel  gear  L.  The 
motion  is  thereby  transmitted  to  the  threaded  spindle  H, 
which  causes  the  nut  G  which  carries  the  pencil  to  move 
upwards.  The  vertical  motion  then  in  this  case  is  proportional 
to  the  load,  and  the  horizontal  one  to  the  extension. 

As  it  is  only  the  relative  motion  of  A  and  B  that  causes  the 
pinion  D  to  rotate,  any  total  displacement  of  the  specimen  will 
not  affect  the  movement  of  the  drum. 


76 


A  HANDBOOK  OF  TESTING  MATEEIALS 


Henning's  Stress-Strain  Recorder  (Fig.  43).— As  the  exten- 
sion of  the  test  bar  previous  to  the  elastic  limit  is  very  small, 
and  after  that  in  the  case  of  ductile  materials  comparatively 


PIG.  43. — Henning's  Portable  Autographic  Stress-Strain  Eecorder. 

large,  the  scale  of  the  load-extension  curve  must  be  a  large 
one  if  the  former  is  to  be  visible.  The  apparatus  here 
described  makes  it  possible  to  reproduce  the  first  part  of  the 
diagram  to  a  large  scale,  the  extensions  after  the  elastic  limit 


STRAIN-MEASUEING  INSTRUMENTS  77 

being  automatically  reproduced  to  a  smaller  one.  It  consists 
of  two  hinged  frames  A  and  B,  one  of  which  is  provided  with 
vertical  rods  N,  and  the  other  with  tubes  N  N'  into  which  these 
fit,  so  that  one  frame  steadies  the  other.  The  length  of  these 
rods  is  such  as  to  keep  the  frames,  at  the  beginning  of  the 
test,  a  fixed  distance  apart,  though  at  the  same  time  they  are 
free  to  move  axially  when  the  specimen  extends.  The  frames 
themselves  are  provided  with  spring-cushioned  bushes  C,  and 
are  hinged  by  taper  plugs  e  and/.  The  bushes  C  are  allowed 
to  move  backwards  and  forwards  by  means  of  the  springs  D. 
Through  these  bushes  pass  the  screws  H,  which  have  hardened 
ends  shaped  like  knife-edges,  and  are  used  to  fasten  the  frames 
to  the  test  bar.  The  lower  frame  A  carries  the  drum  G,  on 
which  the  paper  is  fixed  for  recording  the  test.  The  frame  A 
also  carries  a  parallel  motion,  similar  to  that  on  steam-engine 
indicators.  This  mechanism  rests  on  the  bar  K,  carrying  two 
tubes  L,  which  slide  on  two  rods  L'  screwed  into  the  frame  A 
at  a.  It  is  operated  by  means  of  a  connecting  rod  d  by 
means  of  which  the  relative  motion  between  A  and  B  is  thus 
transmitted  to  the  pencil  on  an  enlarged  scale.  The  wheel  F 
is  also  supported  on  A  by  the  arm  gl,  to  which  it  is  con- 
nected by  a  link  and  screw,  so  that  it  can  swing  to  and  from 
the  marking  point  at  will. 

The  drum  G  is  rotated  by  a  string  which  is  wrapped  round 
it,  one  end  being  connected  to  the  travelling  load,  and  the 
other  to  a  weight  which  keeps  it  tight.  In  using  this  apparatus 
during  a  test,  it  is  necessary  to  keep  the  lever  absolutely 
balanced,  as  if  this  is  not  done  the  increments  of  load  on  the 
diagram  will  not  coincide  with  the  actual  loads  on  the  specimen. 
After  the  yield  point  is  reached,  the  extensions  become  greater, 
so  that  it  is  necessary  to  reproduce  them  to  a  smaller  scale. 
The  hooked  rod  P  is  then  so  adjusted  that  at  this  point  it 
automatically  arrests  the  parallel  motion,  causing  it  to 
slide  on  the  rods  L',  so  that  all  subsequent  extensions  are 
measured  full  size.  The  extensions  previous  to  this  are 
recorded  to  a  scale  of  five  times  full  size.  When  the  test  piece 
breaks,  the  instrument  divides  into  two  parts,  the  rods  N  and 


78 


A  HANDBOOK  OF  TESTING  MATEKIALS 


tubes  L  simply  sliding  out  of  the  tubes  N'  and  rods  L',  while 
the  parallel  motion  is  suspended  from  frame  B  by  means  of  the 
connecting  rod.  Should  it  be  desired  to  use  longer  specimens 
it  is  only  necessary  to  use  a  longer  connecting  rod.  For  com- 
pression tests  a  shorter  connecting  rod  is  used,  so  that  the 
marking  point  will  stand  at  the  top  of  the  drum  at  the 
beginning  of  the  test,  as  its  subsequent  movement  will  then 
be  downwards  in  direction. 

Kennedy's  Autographic  Method. — In  most  autographic 
stress-strain  recorders  the  stress  recording  movements 
depends  on  the  movement  of  the  poise  weight.  Now  it  is 
obvious  that  unless  the  poise  is  absolutely  maintained  the 


PIG.  44. — Kennedy's  Automatic  Stress-Strain  Eecorder. 

diagram  produced  will  not  be  strictly  correct,  hence  attempts 
have  been  made  to  render  the  autographic  apparatus  entirely 
independent  of  the  operator.  Probably  the  instrument  which 
best  fulfills  this  condition  is  that  devised  by  Prof.  Kennedy. 
Fig.  44  illustrates  in  outline  the  method  employed.  A  is  the 
specimen  to  be  tested,  and  this  is  connected  by  suitable  grips  to 
a  second  and  larger  bar  of  mild  steel  B.  The  latter  is  so  chosen 
that  at  the  load  at  which  A  will  break  B  is  well  within  that 
stress  below  which  Hooke's  law  is  exactly  fulfilled.  Attached 
to  B  is  a  "  rolling  pin  "  extensometer  (see  page  58),  and  the 
pointer  C  is  arranged  to  trace  out  a  line  on  a  smoked  glass 
screen  D.  Now  it  is  obvious  that  if  B  is  well  within  the 
elastic  limit,  the  movement  of  the  pointer  C  will  be  exactly 
proportional  to  the  extension  of  B,  which  is  in  turn  propor- 
tional to  the  load  on  both  B  and  A.  The  screen  D  is  attached 
to  a  fine  wire  passing  over  a  pulley  E  and  back  to  the  other 


STEAIN-MEASUEING  INSTEUMENTS 


79 


end  of  the  specimen  under  test.  As  A  extends  it  is  obvious 
that  the  movement  of  the  screen  longitudinally  will  be  pro- 
portional to  this  extension,  and  hence  the  curve  traced  out  by 
the  pointer  C  will  be  a  true  stress-strain  curve  independent  of 
any  other  adjustments  to  the  testing  machine.  There  is  one 
rather  unfortunate  drawback  to  this  apparatus,  and  that  is 


Helical 
Spring 


FIG.  45. — Autographic  Stress-Strain  Eecorder  as  attached  to  a  Single 
Lever  Machine. 


the  fact  that  the  movement  of  C  will  be  in  a  circular  arc.  It 
would  seem  that,  in  spite  of  various  attempts,  this  difficulty 
cannot  be  overcome  without  so  increasing  friction  and  inertia 
as  to  affect  the  accuracy  more  than  is  desirable. 

The  Wicksteed  Recorder. — One  of  the  most  successful 
methods  of  obtaining  an  autographic  diagram  or  stress-strain 
curve  from  single  lever  or  even  multiple  lever  machines  is  to 
place  the  poise  weight  at  a  position  beyond  the  point  of 
maximum  load  and  then  raise  the  end  of  the  beam  slightly 


80 


A  HANDBOOK  OF  TESTING  MATERIALS 


by  means  of  a  helical  spring  fixed  to  a  support  at  the  top. 
It  is  then  obvious  that,  if  a  specimen  be  fixed  in  the  machine 
while  the  poise  weight  is  just  supported  by  the  spring,  the 
load  on  the  specimen  will  be  zero.  If  now  we  begin  to  load 

'/3rprD  Area 


— *i 


Mild  Steel  Specimen 


Extension 
FIG.  46. — Autographic  Diagram,  taken  with  Apparatus  shown  in  Fig.  45. 

the  specimen  by  introducing  water  into  the  hydraulic  cylinder 
or  by  any  other  means  according  to  the  particular  design  of 
machine  employed  it  is  obvious  that  we  tend  to  raise  the 
poise  beam.  Any  upward  movement  of  the  poise  lever, 
however,  shortens  the  helical  spring,  and  hence  reduces  the 
load  carried  by  it.  Hence,  the  unbalanced  load  must  be  taken 


STBAIN-MEASUEING  INSTRUMENTS 


81 


T.M. 


82  A  HANDBOOK  OF  TESTING  MATEEIALS 

up  by  the  specimen.  Now  it  is  obvious  that  since  the  load 
carried  by  the  spring  is  directly  proportional  to  its  extension, 
the  load  carried  by  the  specimen  is  directly  proportional  to 
the  upward  movement  of  the  beam.  It  is  now  a  simple 
matter  to  arrange  that  this  upward  movement  shall  move  a 
pencil  over  a  .drum  while  the  latter  is  given  a  rotary  motion 
by  means  of  an  attachment  to  the  specimen. 

Messrs.  Buckton  have  taken  out  patents  for  applying  this 
principle  by  various  methods  to  their  machines,  of  which 
Fig.  45  can  be  taken  as  typical.  Fig.  46  is  an  autographic 
diagram  taken  on  one  of  these  machines  fitted  with  an 
apparatus  similar  to  that  shown  in  Fig.  45. 

Double  Autographic  Attachment. — Fig.  47  illustrates  yet 
another  method  of  obtaining  stress-strain  diagrams.  It  will 
be  seen  that  there  is  the  usual  autographic  drum  driven  by 
the  movement  of  the  poise  weight,  while  there  are  two  pencil 
gears.  Both  are  worked  through  a  system  of  compound 
levers  from  two  fixed  points  on  the  specimen,  the  relative 
movement  of  which  determines  the  motion  of  the  pencil 
gear.  One  system  of  levers  is  arranged  to  give  a  much 
magnified  movement  for  the  extension  of  the  specimen,  and 
records  extension  below  the  elastic  limit.  The  second  system 
of  levers  is  such  as  will  allow  the  whole  extension  of  the 
specimen  up  to  fracture  to  be  recorded.  It  will  be  seen  that 
there  are  a  number  of  knife-edges  at  each  centre,  so  that  the 
leverage  can  be  varied  to  suit  different  specimens  having 
different  elastic  properties.  It  is,  of  course,  necessary  to 
disconnect  the  first  system  of  levers  when  past  the  elastic  limit, 
otherwise  further  movement  would  smash  the  pencil  gear.  A 
typical  pair  of  stress-strain  curves  are  shown. 


CHAPTEK  V 

METHODS   AND   KESULTS   OF    TESTS    ON    MATERIALS 

Tension  Specimens. — There  are  many  varieties  of  tension 
specimens,  the  size  and  shape  varying  according  to  the  method 
of  testing  and  type  of  machine  to  be  employed.  The  kind  of 


_  p 

>f        o    _ 

t 

v^ 

i 

_/~ 

i 
i 
fe 

i 

f 

~~\ 

\ 

PIG.  48.— Standard  Tension  Specimen  Plate. 

specimen  most  usually  met  with  for  commercial  tests  is  cut 
from  the  rolled  metal,  the  shape  being  shown  in  Fig.  48. 

The   cross-section  is   generally  about   2   inches   by  three- 
eighths,  the  ends,  which  are  clamped  in  the  grips  being  wider 


FIG.  49.— Typical  Tension  Specimen  Bar. 

so  that  the  specimen  is  less  liable  to  break  outside  the  gauge 
length. 

For  bar  tests,  round  specimens  are  employed,  the  ends 
being  gripped  in  V-shaped  grips.  Such  a  specimen  of  normal 
proportion  is  illustrated  in  Fig.  49.  Where  greater  accuracy  is 

G  2 


84 


A  HANDBOOK  OF  TESTING  MATERIALS 


required  the  ends  of  the  specimen  are  threaded,  this  portion 
screwing  into  corresponding  holders,  which  in  turn  are 
fastened  to  the  shackles  by  ball  and  socket  joints.  This  gives 
greater  freedom  in  lining  up,  and  enables  the  load  to  be 
applied  more  nearly  axially  to  the  specimen.  Fig.  50  shows 
the  type  of  end  used  with  the  grip  shown  in  Fig.  17.  The 
actual  length  on  the  specimen  over  which 
the  test  is  made  is  called  the  "gauge 
length."  This  is  most  usually  8  or  10 
inches  on  specimens  of  the  size  already 
illustrated,  but  of  course  tests  are  often 
carried  out  on  specimens  of  much  greater 
length  than  this. 

Standard  Test  Pieces.— The  following 
are  the  recommendations  of  the  Engineer- 
ing Standards  Committee  for  Sizes  of 
Standard  Test  Pieces  : — 

For  Plates  and  other  Structural  Material 
(Test  piece  A,  Fig.  48). 

In  all  cases  L  to  be  approximately  18". 
„        ,,       P     „     not  less  than  9". 
,,        ,,       G     ,,     8 . 

Width  W  for 

pIG    50  _  Screwed  Thickness  over  f"      maximum  width =1J". 
End  for  Tension  or  „         from  f"— £"         „  „     =2". 

Compression Speci-  under  f  „  „     =2j". 

men. 

For  Bars,  Rods,  and  Stays. — (Test  piece  under  1  inch 
diameter)  (Test  piece  B).  Gauge  length  to  be  no  less 
than  eight  times  the  diameter,  and  if  provided  with  enlarged 
ends  to  be  parallel  for  not  less  then  nine  times  the  reduced 
diameter. 

(Test  piece  over  1  inch  diameter)  (Test  piece  F).  Gauge 
length  not  less  than  four  times  the  diameter,  and  if  provided 
with  enlarged  ends  to  be  parallel  for  a  length  not  less  than 
four  and  a  half  times  the  reduced  diameter. 


METHODS  AND  EESULTS  OF  TESTS  ON  MATERIALS    85 
For  Tyres,  Axles,  Forgings,  Castings,  Etc.— 

(Test  piece  C.)     Diameter,  -564"  (J  sq.  in.). 

Parallel  for  not  less  than  2 

Gauge  length,  2". 
(Test  piece  D.)     Diameter,  '798"  (£  sq.  in.). 

Parallel  for  not  less  than  3 

Gauge  length,  3". 


I!  tit 

O  (T)  O 

•*-•      £  ^        tO 

_§        :S  -g    fl 

H  5  g  §  '& 


Should  a  rather  larger  test  piece  than  C  or  D  be  desirable, 
the  following  should  be  adapted  :— 

(Test  piece  E)  Diameter  *977  in.  (f  sq.  in.).  Parallel  for 
not  less  than  4  inches.  Gauge  length  3j  inches. 

Test  of  a  Ductile  Material. — In  a  test  of  this  kind  there 
are  certain  recognised  observations  which  should  be  taken. 
These  are  as  follows  :— 

1.  The  load  at  which  rupture  occurs,  thus  giving  the  break- 
ing stress. 

2.  The  load  at  which  yielding  occurs,  giving  the  yield  point. 

3.  The  elongation  in  the  gauge  length,  giving  the  percentage 
elongation  in  the  stipulated  gauge  length. 

4.  The   reduction  in   the  cross-sectional  area,  giving  the 
percentage  reduction  in  area. 

Observations  before  the  Experiment. — To  enable  these 
observations  to  be  carried  out  the  gauge  length  should  be 
carefully  marked  off.  Measurements  should  also  be  taken  of 
the  diameter  of  the  specimen  if  round,  or  the  breadth  and 
thickness  if  flat.  To  obtain  an  accurate  value,  those  measure- 
ments should  be  taken  in  three  or  more  places,  and  the  mean 
of  these  readings  taken. 

The  specimen  should  also  be  marked  with  some  distinctive 
letter,  number,  or  sign,  so  that  it  may  be  easily  recognisable 
for  future  reference.  This  mark  should  be  made  outside  the 
gauge  length,  preferably  on  one  end  of  the  specimen. 

The  Test. — The  specimen  is  then  placed  in  the  machine, 
and  the  load  gradually  applied.  When  a  certain  load  is 
reached,  it  is  observed  that  the  specimen  suddenly  begins  to 
elongate  very  appreciably  with  the  further  addition  of  little  or 


86 


A  HANDBOOK  OF  TESTING  MATEEIALS 


no  load.  The  point  at  which  this  phenomenon  occurs  is 
known  as  the  yield  point,  and  it  is  said  that  the  "  elastic 
limit  "  has  been  reached.  There  is  no  difficulty  in  recognis- 
ing this  stage  when  reached,  as  the  beam  suddenly  drops 
rapidly,  and  in  consequence  the  pump  has  to  be  worked 
correspondingly  fast  to  keep  the  beam  floating. 

When  the  yielding  stage  is  passed,  the  specimen  continues 
to  stretch  appreciably  as  the  load  is  increased.  As  the 
breaking  point  is  approached  the  specimen  begins  to  draw  out 
at  its  weakest  section,  where  rupture  will  finally  occur.  In 
consequence  of  this  decreasing  cross-sectional  area,  the  load 


ULTIMATE  TENSION  TESTS  AL  I  (Q)  AL  £ '(+)  AL  J/ijV       


EXTENSION  -  INCHES 

FIG.  51.— Ultimate  Tension  Test 
on  Muntz  Metal. 


EXTENSION  -  INCHES 

FIG.    52.— Tension   Tests    on 
Aluminium. 


has  to  be  run  back,  the  maximum  load  which  the  specimen 
maintained  being  noted.  When  the  specimen  is  exhibiting 
these  qualities,  it  is  said  to  be  in  the  "  plastic  stage." 

Eupture  may  occur  without  again  increasing  the  load, 
though  in  some  cases  the  load  has  to  be  run  forward  again 
before  the  specimen  finally  breaks. 

The  characteristic  properties  of  a  material  after  elastic 
breakdown,  and  before  fracture,  are  exhibited  by  the  stress- 
strain  curve,  many  examples  of  which  will  be  found  in  this 
book.  Such  curves  are,  of  course,  either  obtained  auto- 
graphically  or  from  observations  plotted  from  the  readings  of 
the  load  (read  on  machine),  and  the  extension  (read  on  the 
extensometer)  in  the  manner  previously  described.  Figs.  51 


Fractures  of  Wrought-Iron  and  Mild  Steel  in  Tension. 


Fractures  of  Cast-Iron  in  Compression. 


Fractures  of  Cast-iron  Specimens  in  Pure  Torsion. 
PLATE  II. 


PLATE  III. 


METHODS  AND  RESULTS   OF  TESTS  ON  MATERIALS    87 

and  52  show  typical  examples  obtained  by  the  author  during 
tests  on  non-ferrous  metals. 

Observations  after  the  Test.— After  the  specimen  is 
removed  from  the  machine  the  dimensions  at  the  point  of 
rupture  should  be  taken,  so  that  the  reduced  sectional  area 
may  be  calculated.  The  two  halves  of  the  specimen  should 
also  be  fitted  as  accurately  as  possible  together,  and  the  new 
distance  between  the  two  gauge  points  measured. 

Results.— If 

Mean  original  cross-sectional  area  of  specimen  =  AI. 

Gauge  length  of  specimen  =  LI. 

Cross-sectional  area  at  point  of  rupture  =  A2. 

Extended  gauge  length  =  Lg. 

Yielding  load  on  specimen   (i.e.   the  load  at 

yielding  point)  ="  Wi. 

Ultimate  load  on  specimen  =  W2. 

Then  the  percentage  elongation—    2~    ^lOO. 

The  percentage  reduction  in  area—    2~    ^lOO. 

Stress  at  yield  point  on  original  area—  -r-1. 

Ultimate  stress  or  breaking  stress  on  contracted  area—  -p  • 

A2 

Usually  the  units  employed  are  the  inch  and  the  pound,  and 
the  stresses  are  therefore  calculated  in  pounds  per  square  inch. 

Characteristics  of  Rupture. — Mild  steel  and  good  wrought- 
iron  show  much  contraction  at  the  point  of  rupture.  Stronger 
steels  are  less  ductile.  Brass  is  a  very  ductile  material,  and 
exhibits  a  silky  section  when  broken  (see  Plates  II.  and  III.). 

Distribution  of  Extension. — Let  the  gauge  length  of  the 
specimen  be  divided  into  equal  divisions  before  testing.  After 
rupture  has  taken  place  the  extension  in  each  division  is 
measured,  and  plotted  as  ordinates  on  a  base  line  representing 
the  equal  divisions  on  the  specimen.  Fig.  53  shows  the  curve 
obtained  from  a  ductile  material.  The  distribution  of  extension 


88 


A  HANDBOOK  OF  TESTING  MATERIALS 


w     S 

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The  table  gives  the  results  obtained  on  five  different  materials,  and  may  be  taken  as  typical  of  the  method  of 
recording  commercial  tension  tests.  It  will  be  seen  that  the  loads  usually  recorded  are  those  noted  at  the  yield 
point  and  the  maximum  load.  The  other  measurements  made  will  be  seen  from  the  table. 

cS 

3  5  i 

03      O 

1  Reduction  of 
Area. 

Zl 

§    §    8 
8    8    8 

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Reduced  Area. 

1 

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5    1    § 

CO          CO 

1 

1  §  3 

1  I 

Extension. 

21 

s  s  s 

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3  § 

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Ai       *1       <M       AH       CO 

Maximum  Load. 

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METHODS  AND   KESULTS  OF  TESTS  ON  MATERIALS    89 

is  not  at  all  uniform,  but  increases  very  greatly  towards 
that  section  where  fracture  occurs. 

This  indicates  the  importance  of  specifying  over  what  gauge 
length  the  percentage  elongation  is  taken,  since  the  smaller 
the  gauge-length  the  greater  is  the  percentage  elongation. 

Tests  of  Non-Ductile  Materials. — Cast-iron  furnishes  one  of 
the  best  examples  of  non-ductile  materials.  Such  materials 
have  no  elastic  limit,  nor  appreciable  yield  point.  When 
testing,  it  is  of  great  importance  that  no  bending  be  set  up 


f 

>-- 

N 

/ 

X 

-x^ 

7 

"^*-- 

__ 

2 

, 

! 

PIG.  53. — Distribution  of  Extension. 

due  to  imperfect  clamping  in  the  shackles,  as  this  would 
materially  distort  the  result.  The  best  way  to  ensure  perfect 
alignment  is  to  employ  the  ball  and  socket  tension  joint 
already  described. 

TYPICAL  EESULT— CAST-IRON. 

Mark.  Diameter.         Area.  Maximum  Load.  Maximum  Stress. 

1  0.1.  -750  -442  5-94  tons.         13'43  tons  per  sq.  in 

Compression  Tests. — The  specimens  for  compression  tests 
are  generally  short  cylinders,  a  very  usual  size  being  1J 
inches  long  by  f  inch  in  diameter,  as  shown  in  Fig.  54. 
Whatever  may  be  the  size  of  specimen  chosen,  however, 
it  should  be  taken  as  a  general  rule  that  when  only  the 
ultimate  strength  is  to  be  determined  the  length  should  not 


90 


A  HANDBOOK  OF  TESTING  MATEEIALS 


exceed  two  to  three  times  the  diameter.  If  this  ratio 
of  length  to  diameter  be  exceeded,  bending  of  the  specimen 
may  occur,  so  that  its  failure  may  be  due,  not  to  com- 
pression alone,  but  to  a  combination  of  compression  and 
bending.  For  purposes,  other  than  ultimate  resistance  tests, 
specimens  of  1  inch  diameter  and  10  or  20  inches  in  length 


FIG.  55. — Short  Ductile   Specimen 
in  Compression. 


FlG.  54.  —  Typical 
Compression  Speci- 
men. 


FIG.  56.— Ball  and  Socket  Joint. 


may  be  used.  Great  care  must  be  taken  to  ensure  axial 
loading. 

The  Test. — The  machine  is  fitted  up  for  compression  tests, 
and  the  specimen,  after  its  length  and  diameter  have  been 
carefully  measured,  is  inserted  between  hardened  steel  plates. 
It  is  preferable  to  have  one  of  these  plates  fitted  with  a  ball 
joint  (Fig.  56)  as  then  the  pressure  is  distributed  evenly  over 
the  two  faces  of  the  specimen. 

The  load  is  applied,  and  increased  by  equal  increments,  the 
length  of  the  specimen  together  with  its  mean  diameter  being 
measured  in  each  case. 


METHODS  AND   EESULTS  OF  TESTS   ON  MATEEIALS    91 

This  mean  diameter  is  a  somewhat  indeterminate  quantity. 
An  easier  method  of  obtaining  this  dimension  is  as  follows  : — 

In  Fig.  55  let  ai  and  li  be  the  mean  diameter  and  length 
respectively  of  the  specimen  before  testing. 

Let  a2  and  Z2  be  the  new  dimensions  after  a  certain  load  is 
applied.  Then  since  the  volume  of  the  specimen  remains 
approximately  constant, 


Hence  «2— 


Consequently  all  that  it  is  necessary  to  do  after  each  new 
load  is  applied  is  to  measure  the  new  length,  from  which  the 
new  mean  diameter  can  be  obtained  from  the  above  simple 
equation.  The  length  of  the  specimen  can  be  measured  by  a 
scale  and  vernier  without  removing  the  specimen  from  the 
machine.  Owing  to  the  fact  that  the  specimen  continues  to 
compress  for  some  time  after  each  load  is  applied,  it  is  important 
that  a  stipulated  and  definite  time  should  elapse  between  the 
application  of  each  new  load  and  the  corresponding  reading  of 
the  new  length. 

A  typical  table  of  readings  is  given  below  :  — 


SPECIMEN  —  MILD  STEEL. 
Dimensions  —  Diameter,  f  ''  ;  Length, 


Load  in  Ibs. 

Total 
Compression. 

New  Length, 
li  in  inches. 

New  Area, 

«,  =  «£ 

Real  Stress 
Load,, 
-^-Ibs.persq.in. 

0 

•000 

1-500 

•4-12 

0 

6,000 

•006 

•494 

•444 

13,520 

12,000 

•013 

•487 

•446 

26,900 

15,000 

•016 

•484 

•447 

33,550 

18,000 

•057 

•443 

•459 

39,220 

24,000 

•098 

•402 

•472 

50,750 

30,000 

•167 

•333 

•497 

60,350 

36,000 

•251 

1  -249 

•531 

67,800 

42,000 

•343 

1-157 

•573 

73,400 

51,000 

•478 

1-022 

•648 

78,750 

57,000 

•523 

0-977 

•678 

84,200 

66,000 

•662 

0-838 

•791 

83,500 

92 


A  HANDBOOK  OF  TESTING  MATERIALS 


Curves  plotted  from  these  figures  are  shown  in  Fig.  57.  It 
will  be  observed  that  yielding  takes  place  at  a  load  of  about 
15,500  Ibs.,  giving  a  stress  on  the  specimen  of  34,500  Ibs. 
per  sq.  in. 

Appearance  of  Specimen. — As  the  tests  on  the  mild  steel 


MlL-D     5TEEL.. 

TEST 


•o 

INCHES. 


FIG.  57. — Real  and  Apparent  Stress-Strain  Curves  in  Compression 
(from  single  observations). 

proceeds  the  specimen  is  seen  to  bulge,  finally  assuming  a 
barrel-shaped  form,  and  if  the  load  is  increased  to  a  sufficiently 
large  extent,  cracks  and  seams,  approximately  parallel  to  the 
axis  of  the  specimen,  appear  as  seen  in  Fig.  58. 

Wrought-iron  would  show  very  much  the  same  character- 
istics, except  that  the  cracks  would  probably  be  more 
pronounced. 


METHODS  AND   EESULTS  OF  TESTS   ON  MATERIALS    93 


Cast-iron. — If  cast- 
iron  be  tested  in  com- 
pression, failure  will 
occur  in  a  very  different 
way  from  that  of 
wrought-iron  or  mild 
steel,since  the  specimen 
fails  by  shearing.  To 
thoroughly  understand 
this,  it  is  necessary 
to  inquire  into  the 
manner  in  which 
the  shear  stress 
varies  on  planes  in- 
clined to  the  axis 
through  which  the 
pressure  acts. 


FIG.  58. — Appearance  of  Ductile  Compression 
Specimen  at  Failure. 


Let  a  =  cross-sectional  area  of  the  specimen. 

Let/  =  intensity  of  stress  on  planes  normal  to  axis. 

Eesolve  this  stress  into 
forces  parallel  and  per- 
pendicular to  plane  A,  B 
(Fig.  59). 

Then     shear    force    on 
plane  AB  =  f.a.  cos  6. 
B  But  area  of  plane  AB  = 

rf  I       ^<  a 


sin  6 

. ' .  Shearing    stress    on 

plane    AB  =  /•*•  cos  e  = 
a 

sin  6 
f  cos  6  sin  6. 

From  which  it  is  seen 
that  the  shear  stress  is  a 
maximum  when  6  =  45°. 


FIG.  59. — Shear  Stress  on 
Cast-iron. 


94 


A  HANDBOOK  OF  TESTING  MATERIALS 


Theoretically,  therefore,  fracture  should  take  place  along  a 
plane  inclined  at  45°  to  the  axis.  This  is  found  to  be  so,  or 
very  nearly  so,  in  practice,  any  deviation  from  theory  being 


FIG.  60. —  Frac- 
ture of  Ductile 
Material  in^Ten- 
sion. 


FIG.  6 1 . — Fracture 
of  Cast-iron  in 
Compression. 


probably  due  to  non-uniformity  in  loading,  local  variation  in 
the  material,  or  possibly  to  internal  friction. 

Brittle  hard  materials  all  behave  in  this  way,  while  ductile 
plastic  metals  fail  similarly  to  mild  steel. 

Cast-Iron  in  Compression. — If  the  fracture  of  a  ductile 
specimen,  which  has  been  broken  by  application  of  a  direct 


METHODS  AND  BESULTS  OF  TESTS  ON  MATEEIALS    95 


pull,  be  examined,  it  will  be  found  that  failure  has  not  been 
the  result  of  tearing  across  a  plane  section  perpendicular 
to  the  axis,  but  that  shearing  has  taken  place  along  the 
surface  of  a  cone  of  semi-vertical 

angle,  approximately  j  (Fig.  60). 

If  a  specimen  of  the  same  material 
be  taken  and  tested  in  compression 
it  will  be  found  that,  if  the  speci- 
men is  too  short  for  buckling 
to  take  place,  there  will  be  no 
definite  fracture  (Fig.  58).  A 
possible  explanation  is  that,  when 
the  specimen  is  short  enough  for 
buckling  not  to  occur  it  is  too 
short  for  shearing  to  take  place 
in  one  fracture.  There  will 
therefore  be  an  internal  crumbling 
along  numerous  shearing  planes, 
which  in  a  plastic  material  may 
not  exhibit  itself  as  a  separation 
of  the  specimen  into  so  many 
pieces.  In  a  brittle  material 
(Fig.  61)  the  shearing  fracture 
produced  by  direct  compressive 
stress  is  very  marked.  So  far, 
then,  we  may  say  that  in  at  least 
ductile  materials,  directly  stressed, 
shearing  is  the  governing  factor. 
Let  us  examine  how  such  a 
stress  arises  and  what  its 
magnitude  will  be.  Consider  a 

specimen  of  unit-cross-section  subjected  to  a  steady  pull  of 
P  Ibs.  (Fig.  62).  Then  on  any  section  perpendicular  to  the 
axis  there  will  exist  a  tensile  stress  numerically  equal  to  P. 
On  this  plane  there  will  be  no  tangential  stress  since  P  can 
have  no  component  at  right  angles  to  itself.  On  a  plane 


FIG.  62.  —  Eesolution  of 
Forces  in  a  Specimen  sub- 
jected to  Tension. 


96  A  HANDBOOK  OF  TESTING  MATERIALS 

section  inclined  to  the  axis  there  will,  however,  be  in  general 
two  stresses,  one  normal  and  the  other  along  the  plane  of  the 
section.  Consider  the  equilibrium  of  one  of  the  portions  cut 
off  by  the  plane  of  section.  We  have  along  the  axis  a  stress 
=  P,  along  the  plane  a  shearing  stress,  say,  q,  and  perpen- 
dicular to  it  a  normal  stress,  say  r.  These  three  must 
equilibrate. 

Eesolving  vertically  we  have 

r    .  sin  0+  -3—  cos  6=P  or  r-\-q  cot  0=P  ...  (1) 

sin  0  sin  6 

Eesolving  horizontally  we  have 

—  —  cos  e=-2—  sin  GOT  q=r  cot  B  ...  (2) 

sin  &  sin  0 

whence  r  =  P  sin2<9  (3) 

and  q  =  P  sin  0  cos  6  ......         (4) 

p 
This  last  equation  may  be  written  as  q=  ^  sin  20.      The 

maximum  value  of   sin    20   is    1    and   occurs   when   0=^. 

Hence  we  see  that  a  direct  stress  induces  shear  on  planes 
inclined  to  the  axis  and  that  this  shear  stress  is  a  maximum 
on  planes  inclined  at  45°  to  the  axis,  or  their  envelopes  (cones 

of  semi-vertical  angle  ^).     Its  value  is  then  half  the  maximum 

direct  stress.  Therefore  if  no  disturbing  factors  enter  into  the 
question  a  directly  stressed  specimen  should,  if  the  shearing 
stress  is  the  determining  factor,  shear  along  a  surface  inclined 
at  45°  to  the  axis.  The  symmetrical  surface  fulfilling  this 


condition  is  a  cone  of  semi-vertical  angle  =2-     This  fracture 

allows  separation  in  the  case  of  a  tension  specimen,  but  not 
so  in  the  case  of  compression.  A  specimen  fractured  by  direct 
push  therefore  separates  along  a  plane  surface. 

It  has  already  been  indicated  that  the  measurement  of  this 
angle  of  yield  for  a  ductile  specimen,  subjected  to  compression, 
presents  very  considerable  difficulties.  In  the  case  of  tension 
the  difficulties,  though  less  manifest,  are  none  the  less  real. 
The  conical  fracture  is  very  apparent,  and  the  measurement 


METHODS  AND  EESULTS  OF  TESTS  ON  MATERIALS    97 

of  the  angle  is  easy  ;  it  must,  however,  be  remembered  that 
the  angle  which  can  be  measured  gives  only  an  approximate 
indication  of  the  form  the  conical  surface  assumed  when  the 
material  yielded,  and  was  virtually  destroyed.  When  the 
yield  point  is  passed  the  material  offers  no  permanent 
resistance  to  the  application  of  the  force ;  it  is,  in  effect,  a 
liquid,  and  the  increase  of  the  force  merely  shortens  the  time 
occupied  in  viscous  flow,  and  until  actual  surface  separation 
must  take  place.  The  plastic  drawing  out  will  deform  the 
surface  along  which  yield  takes  place  and  which  probably  also 
forms  the  surface  of  separation. 

In  a  ductile  material  it  is,  therefore,  as  has  been  seen,  a 
matter  of  no  little  difficulty  to  determine  exactly  the  surface 
along  which  yielding  occurs.  In  a  brittle  material  under 
compression  the  problem  is  considerably  simpler,  and  its 
consideration  may  throw  some  light  on  what  really  happens 
within  a  stressed  material.  In  a  specimen  of  cast  iron 
the  fracture  is  perfectly  definite,  and,  as  no  plastic  flow 
occurs,  it  may  be  assumed  that  the  surface  of  yield  coin- 
cides with  the  surface  of  separation.  Therefore  if  the 
maximum  value  of  the  shear  stress  is  the  only  determining 
factor,  the  fracture  should  take  place  along  a  plane  inclined 
to  the  axis  at  exactly  45°.  This  is  never  found  to  occur  ;  the 
angle  6  is  consistently  less  than  45°,  and  a  reason  has  to  be 
sought. 

Let  us  examine  the  following  results  obtained  on  a  specimen 
of  cast  iron. 

Diameter  —  '727  inch. 

Length  =  2*125  inches. 

Breaking  load  =  19'25  tons. 

0  —  33°. 
Maximum  shear  stress  on  plane — 

where  6  =  45°  =  23'2  tons  per  sq.  inch. 

Direct  stress  on  this  plane  =  23'2  tons  per  sq.  inch. 

Shear  stress  on  plane  of  fracture •=  21*2  tons  per  sq.  inch. 

Direct  stress  on  plane  of  fracture  =  13'7  tons  per  sq. 
inch. 

T.M.  H 


98  A  HANDBOOK  OF  TESTING  MATERIALS 

It  will  be  seen  that  fracture  took  place  along  a  surface 
where  the  shear  stress  was  2  tons  per  sq.  inch  below,  or, 
roughly,  10  per  cent,  lower,  than  the  maximum.  It  will, 
however,  be  noticed,  that  the  normal  stress  on  the  breaking 
section  was  considerably  lower  than  that  on  the  section  where 
the  shear  stress  was  a  maximum.  This  immediately  suggests 
the  fact  that  a  direct  push  between  two  surfaces  increases  the 
resistance  to  their  shearing  or  sliding  over  one  another.  The 
effect,  in  fact,  is  very  akin  to  friction,  and  a  theory,  usually 
known  as  Navier's  theory,  has  been  developed  on  these  lines, 
and  is  as  follows. 

Let  the  true  shear  resistance,  when  no  normal  stress  is 
exerted  between  the  surfaces,  be  f.  Then  if  r  is  the  normal 
stress  on  the  section,  we  may  suppose  that  the  actual 
shearing  resistance  offered  (q)  is  of  the  form  q=f+n  r  ; 
but  q  =  P  sin  d  cos  0,  and  r  —  P  sin  20.  /.  /  =  P  (cos  6  sin  d 
-  p  sin2<9). 

Fracture  will  take  place  across  the  section  where  /  is  a 

maximum,  i.e.,  where  -j^=0. 
du 

df 

^jj==P  cos  Q  (cos  d— n  sin  0)+P  sin  0  (—sin  6— /*  cos  0}  =  0. 

. ' .  cos20— sin20— 2  n  sin  6  cos  0.     i.e.,  /x=cot  20. 

If  4> Bangle  of  friction,  then  tan  <j>=cot  20. 

•••  20+«>=~,  and  «=j-* 

Taking  the  particular  case  where  6  —  33°,  we  have  0  =  24° 
or  ju  =  *45  approximate.  Whether  this  theory  is  at  ail 
justifiable  is  for  future  research  to  determine. 

The  following  values  have  been  obtained  from  compression 
tests  on  cast-iron  specimens.  It  will  be  a  good  exercise  for 
the  student  to  measure  the  angles  of  fracture  and  evaluate  the 
co-efficient  /x.  It  should  be  remembered  that  discrepancies 
may  be  due  to  (1)  non-homogeneous  material ;  (2)  the  fact 
that  yield  point  and  ultimate  fracture  loads  are  not  neces- 
sarily co-incident.  This  may  account  for  the  varying  results 
recorded  in  the  following  table. 


METHODS  AND  RESULTS  OF  TESTS  ON  MATERIALS    99 


TABLE   II. 
COMPRESSION  TESTS  ox  CAST-!ROX. 


D  in 
inches. 

Liu 

inches. 

W  in  tons. 

*-I 

in  tons 
per  sq.  inch. 

Q  in 

degrees. 

/« 

fin  tons 
'  per  sq. 
inch. 

•916 

1-662 

37-09 

56-3 

29 

•625 

15-6 

•752 

1-470 

22-15 

49-9 

34 

•404 

16-8 

•966 

1-675 

41-65 

56-8 

33 

•445 

18-5 

•904 

•807 

26-89 

41-9 

30 

•577 

12-1 

•815 

•760 

28-61 

55-0 

31 

•532 

16-5 

•943 

•652 

27-33 

39-1 

28 

•675 

10-4 

•816 

•762 

26-92 

51-5 

28 

•675 

13-6 

•961 

•663 

33-^6 

46-1 

28 

•675 

12-2 

Autographic  Diagrams. — An  autographic  diagram  gives 
much  fuller  information  as  to  the  behaviour  of  a  metal 
under  test  than  does  the  mere  breaking  test. 

Not  only  does  it  give  all  the  results  obtainable  from  a  test 
to  rupture,  but  in  addition  the  extension  of  the  bar  at  any 
load  can  be  easily  obtained  from  it,  together  with  the  work 
expended  in  breaking  the  bar. 

Before  taking  the  diagram  the  necessary  measurements  of 
gauge  length  and  cross-sectional  area  of  the  specimen  are 
made.  The  specimen  is  clamped  in  the  grips  and  the 
autographic  apparatus  fitted.  The  load  is  then  run  on  slowly, 
the  beam  being  kept  floating  by  means  of  the  pump.  Great 
care  should  be  exercised  to  prevent  the  beam  touching  the 
stops,  otherwise  the  diagram  produced  will  not  be  a  true  one. 
This  difficulty  will  be  particularly  pronounced  at  the  yield 
point  and  near  the  point  of  rupture.  At  the  yield  point,  owing 
to  the  comparatively  rapid  change  in  length  of  the  specimen, 
the  pump  has  to  be  worked  continuously  with  little  or  no 
increase  in  load.  Nearing  the  rupture  point  with  ductile 
materials  the  load  has  actually  to  be  run  back  owing  to  the 
rapidly  diminishing  cross-sectional  area  of  the  specimen. 

It  was  stated  previously  that  the  load  was  run  on  and  the 
beam  kept  in  equilibrium  by  means  of  the  pump.  This,  in  a 
sense,  is  hardly  true  when  the  pump  is  worked  from  the  shop 

H  2 


100 


A  HANDBOOK  OF  TESTING  MATERIALS 


shafting.  When  such  is  the  case  it  can  only  be  operated  at 
some  definite  speed,  so  that  the  beam  is  kept  floating  by  the 
rate  at  which  the  load  is  applied. 

Fig.  63  shows  a  typical  diagram  for  mild  steel  plates. 

If  the    cross-sectional    dimensions    of    the    specimen    be 


3 


fi 

2 

-  o 

Q 


0 
•  J 


^ 


V 


MILD  STEEL  PLATES 


TENSION  TEST 


05 


25 


•JO  -;5  -20 

£TxT£T/S/S/OA/  -    INCHES 
FIG.  63.— Mild  Steel  Plates  in  Tension  (Autographic  Diagram). 

measured  at  definite  loads  during  the  tests,  a  means  is  given 
of  determining  the  actual  stresses  on  the  reduced  section  of 
the  bar. 

A  second  curve  plotted  from  results  obtained  thus  is  shown 
in  Fig.  64. 

Raising  the  Yield  Point. — The  autographic  diagram  affords 
a  very  convenient  method  of  verifying  the  statements  regard- 
ing the  raising  of  the  yield  point  by  a  process  of  repeated 
loading.  The  phenomenon  is  as  follows :  Let  the  load  be 


METHODS  AXD  RESULTS  0£   TES'JJS  j^T/MljBJSiALS  101 


carried  a  little  beyond  the  initial  elastic  limit,  and  allowed  to 
remain  so  for  a  certain  time.  On  removing  the  load,  and  then 
again  running  it  on,  the  specimen  will  be  found  to  yield  not 


MILD     STEEL 
Autographic  Diagram. 
Mean  D!a.=-90B"    • 
Gauge  L ength  -8* 


Elongation  —  inches. 
FIG.  64. — Curves  of  Eeal  and  Apparent  Stress. 

at  the  initial  or  primitive  elastic  limit,  but  at  about  the  load 
originally  applied  to  the  specimen.  By  such  a  process  the 
elastic  limit  may  be  raised  until  finally  it  coincides  with  the 
breaking  load  of  the  specimen.  This  is  shown  in  Fig.  65. 


102  4-8  VNI)BQOK0  OF  TESTING  MATERIALS 

This  phenomenon  of  raising  the  yield  point  by  repeat  loadings 
is  but  one  of  a  number  which  can  be  conveniently  investigated 
by  the  student.  For  a  full  discussion  of  the  change  of  elastic 
properties  by  mechanical  and  heat  treatment  the  student 
should  refer  to  proceedings  of  scientific  and  technical  societies. 
It  will  suffice  to  give  here  a  few  typical  examples  together  with 


Extension  -  Inches 

FIG.  65.— Autographic  Diagram  of  Mild  Steel  in  Tension,  showing  Effect 
of  removing  temporary. 

the  corresponding  stress  strain  curves  obtained  by  the  author 
and  his  students. 

The  Elastic  Range.— The  theory  was  enunciated  by 
Bauschinger  that  a  change  in  the  elastic  limit  follows  the 
extension  of  a  specimen,  and  that  if  mild  steel  has  an  elastic 
limit  of,  say,  13  tons  in  a  tension  test,  and  the  same  value  in  a 
compression  test,  then  if  the  material  be  overstrained  in 
tension  until  the  new  elastic  limit  is  raised  to,  say  16  tons,  the 
olaetic  limit  in  compression  will  be  10  tons.  In  other  words, 


METHODS  AND   EESULTS  OF  TESTS  ON  MATERIALS  103 


the  elastic  range  of  the  material  is  26  tons.  In  July,  1908,  the 
author  made  tests.  Stress  distribution  was  not  taken  into 
account,  and  the  results  are  therefore  not  within  an  accuracy 
of  5  per  cent.  The  first  elastic  limit  was  13  tons.  By 
increasing  the  tension  elastic  limit  2*7  tons,  the  compression 
elastic  limit  was  lowered  2'5  tons.  A  full  account  of  these 


25 


20 


Specimen  HTS  I. 
Tension  Test. 


A.  Primary  Test. 

B.  35mi'ns.afterA. 

C.  7  days  after  B. 

D.  20 m ins.  after  C. 
L^/lfier  10  m/ns.  at  100"  C, 

F.  Se/ays  after  E. 

G.  After  /O  mins.  at  100" C. 


FIG.  66. — Effect  of  Time  and  Low  Heat  Treatment  on  Mild  Steel  in  Tension. 

tests — considered  unsatisfactory  for  various  reasons  set  forth 
—are  to  be  found  in  the  Journal  of  the  Institution  of  Junior 
Engineers,  July,  1909. 

Mr.  Leonard  Bairstow,  shortly  afterwards,  published  in 
Yol.  OCX.,  Series  A,  of  the  Philosophical  Transactions  of  the  Royal 
Society  a  valuable  contribution.  He  noticed  that  fatigue  was 
able  to  produce  slow  yielding  whenever  the  compressive  and 
tensile  stresses  were  not  equal,  even  though  the  maximum 
stress  applied  was  considerably  below  the  yield  stress. 


104 


A  HANDBOOK  OF  TESTING  MATERIALS 


Time  Effect.— If  a  mild-steel  specimen  be  tested  up  to  just 
beyond  its  elastic  limit,  and,  after  removing  the  load,  allowed 
to  stand,  it  will  be  found  to  recover  its  elastic  properties  with 
time,  and  on  again  testing,  the  elastic  break-down  point  will 
be  found  to  be  raised. 

Effect  of  Low  Temperature  Heat  Treatment.— This  same 
recovery  of  elastic  properties  is  even  more  marked  if  the 


A.  Primary    Test 

B.  3  Weeks  after  A 

C .  dfter  15  mins.  at  100  °C 


FIG.  67. — Effect  of  Time  and  Boiling  on  Mild  Steel  Specimen  in 
Compression. 

specimen  be  boiled  at  100°  C.  for  a  short  time.  Both  time 
and  heat  treatment  effects  are  shown  in  Fig.  66.  The  specimen 
was  a  sample  of  high  tenacity  steel  of  remarkably  uniform 
properties.  The  data  in  connection  with  the  method  of 
treatment  is  given  on  the  curve.  A  similar  phenomenon  is 
observed  both  in  compression  and  tension  tests.  Fig.  67  shows 
a  typical  curve  obtained  with  mild  steel  in  compression. 

Effect  of  High  Temperature  Heat  Treatment. — This 
phenomenon  is  discussed  in  Appendix  IV.  The  curves  shown 
in  Fig.  68  are  those  obtained  from  the  same  material  but 
subjected  to  various  high  temperature  heat  treatments.  It 


\L 


30  BN 


30  BA 


50 


300 


00  150  200  250 

EXTENS/ON  (UNIT  =  -0001  INCH) 
FIG.  68.— Curves  showing  Effect  of  Heat  Treatment  on  Bessemer  Steel. 


350 


106 


A  HANDBOOK  OF  TESTING  MATEEIALS 


will  be  observed  that  there  is  a  great  change  in  the  elastic 
properties  of  the  Bessemer  steel  thus  treated.  Eeferences  to 
the  tests  will  be  found  on  p.  260. 

Mechanical  Hysteresis. — If  a  specimen  be  loaded  up  past 
a  certain  point  (in  general  below  the  elastic  limit)  and  then 


2,000 


80  120  160  200  240  280 

I  -    ORIGINAL  STRESS-STRAIN  CURVE.DEC.  7TH    1901* 

II  -    IMMEDIATELY  AFTER  NO.  1. 
•  II  -    JANUARY  15TH   19O2 

IV  .FEBRUARY  23RD  19O2 

FIG.  69. — Curves  showing  Mechanical  Hysteresis, 
the  load  be  decreased  and  readings  of  extension  be  taken  both 
during  increasing  and  decreasing  load  we  get  the  phenomenon 
known  as  mechanical  hysteresis.  That  is  to  say,  the  two 
curves  for  increasing  and  decreasing  load  do  not  coincide  but 
enclose  area  as  shown  in  Fig.  69.  Professor  Coker  has 
made  many  interesting  researches  on  this  phenomenon,1  and 

1  On  the  effect  of  low  temperature  on  the  recovery  of  overstrained  iron 
and  steel.     Physical  Review,  Vol.  XV.,  1902. 


METHODS  AND  EESITLTS   OF  TESTS  ON  MATEKIALS  107 

the  curves  reproduced  are  from  some  of  his  results  obtained 
on  mild  steel.  His  object  was  to  determine  the  effect  on 
mechanical  hysteresis  of  time.  It  will  be  seen  on  comparing 
the  curve  in  Fig.  69,  and  the  data  given  immediately  below  it, 
that  the  effect  of  time  is  to  increase  the  hysteresis.  This 
hysteresis  is  probably  due  to  friction  between  the  particles  of 
the  metal  moving  relative  to  one  another  under  strain. 

Further  data  as  to  the  effect  of  time,  etc.,  will  be  found  on 
consulting  the  proceedings  of  the  engineering  institutions. 
Some  curves  are  also  given  in  Chapter  VI.  showing  these 
phenomena  as  exhibited  with  torsion  specimens. 

Modulus  'of  Elasticity,  E. — The  modulus  of  elasticity,  or 
Young's  Modulus  is  the  ratio  of  stress  to  strain  within  the 
elastic  limit.  Suppose  a  specimen  be  tested  to  the  elastic 
limit  and  by  some  means  a  curve  is  obtained  with  the  extensions 
of  the  specimen  as  abscissae,  and  the  loads  causing  these 
extensions  as  the  ordinates. 

load 


x,        -r,     stress     sectional  area  of  bar 
Now  E=-r — —  =  -— 

strain  extension 


original  length 
load          original  length 
"extension      sectional  area 
. ' .   E  =  slope  of  the  load-strain  line  multiplied  by  a  constant. 

From  which  simple  equation  E  can  be  found. 

The  load-strain,  or  as  it  is  somewhat  loosely  called,  the 
stress-strain  line,  is  obtained  by  some  form  of  extensometer. 

For  such  work  round  specimens  are  almost  invariably  used, 
as  they  can  be  turned  and  measured  very  accurately. 

The  Experiment  to  Find  the  Yalue  of  E. — The  specimen  is 
marked  off  for  the  reception  of  the  extensometer,  the  gauge 
length  and  cross-sectional  area  being  accurately  determined. 

The  extensometer  is  then  clamped  on  to  the  specimen,  the 
latter  being  placed  in  the  testing  machine,  and  a  small  load 
applied  to  steady  the  whole.  The  load  is  then  run  on  in 
equal  increments,  measurements  of  the  extensions  of  the 
specimen  being  taken  in  each  case  by  the  extensometer. 


108 


A  HANDBOOK  OF  TESTING  MATERIALS 


When  the  maximum  load  is  reached,  the  load  is  reduced  by 
equal  decrements,  readings  of  the  extensometer  being  taken  as 

before. 

A  curve  is  then  plotted  between  the  loads  and  extensions,  both 
for  ascending  and  descending  values  of  the  load,  Such 
curves  for  mild  steel  are  shown  in  Fig.  70.  The  curves  are 
straight  lines,  proving  that  within  the  elastic  range  the  stress 
is  proportional  to  the  strain. 


MILD   STEEL. 

Gftuce  LENGTH  * 
Seer.  &f*£&*  7" 


ool  -ooa  -c 

EXTENSION     IN    INCHES 

FIG.  70.— Mild  Steel  in  Tension. 


The  slope  of  curves  =  tan  6  =  .  =•  1,345  inch  ton 


units. 

The  cross-sectional  area  of  the  specimen  =  "768  sq.  in. 
The  gauge  length  =    8  inches. 

'.'    E  =  l,  845X^  =  14,000  tons  per  sq.  in.,  or  31,400,000 
*  /  uo 

Ibs.  per  sq.  in. 


METHODS  AND   EESULTS   OF  TESTS  ON  MATERIALS  109 

The  following  tests  were  made  with  the  Ewing  extensometer, 
and  the  tables  indicate  how  results  of  such  tests  should  be 
set  out. 

Specimen  I. — Brass  Rod. 

Observations. 

Distance  between  gauge  marks  on  specimen,  8  inches. 
Leverage  of  machine,  22*4. 
Value  of  1  division  on  microscope  scale,  0*0002. 
Diameter  of  specimen,  '3755,  '875,  '375  inches. 
Mean  diameter  of  specimen,  '375  inches. 


Load. 
Lbs. 

Ktading  on  Scale. 
(Loading.) 

Readings  on  Scale. 
(Unloading.) 

Extensions. 
Inches. 

10 
20 
30 
40 
50 
60 
70 
80 
90 
95 

21 
26 
32 
36 
42 
47 
52 
57 
62 
68 

21 
26 
31 
36 
41 
46 
51 
56 
61 
68 

•0010 
•0011 
•0009 
•0011 
•0010 
•0010 
•0010 
•0010 
•0013 

85 

Totals. 

•0094 

Specimen  II. — Hard  Steel  Rod. 

Observations. 

Distance  between  gauge  marks  on  specimen,  8  inches. 
Leverage  of  machine,  22*4. 

Value  of  1  division  on  microscope  scale,  0'0002  inches. 
Diameter  of  specimen,  '358,  *356,  *356  inches. 
Mean  diameter,  '357  inches. 


110 


A  HANDBOOK  OF  TESTING  MATERIALS 


Load. 
Lbs. 

Reading  on  Scale. 
(Loading.) 

Reading  on  Scale. 
(Unloading.) 

Extensions. 
Inches. 

10 
20 
30 
40 
50 
60 
70 
80 
90 
95 
100 

28 
31 
34 
37 
40 
43 
46 
49 
52 
53-5 
55 

28 

31 
34 
37 
•      40 
43 
46 
49 
52 
53-5 
55 

•0006 
•0006 
•0006 
•0006 
•0008 
•0006 
•0006 
•0006 
•0003 
•0003 

90 


Totals. 


•0054 


Specimen  III.— Mild  Steel. 

Observations. 

Distance  between  gauge  marks  on  specimen,  8  inches. 
Leverage  of  machine,  22*4  inches. 
Value  of  1  division  on  microscope  scale,  0'0002. 
Diameter  of  specimen,  '374,  '374,  '374  inches. 
Mean  diameter,  '374  inches. 


Load. 
Lbs. 

Reading  on  Scale. 
(Loading.) 

Readinc  on  Scale. 
(Unloading.) 

Extensions. 
Inches. 

10 

3-9 

3  '75 

•00055 

20 

4-2 

4-00 

•00055 

30 

4-4 

4-35 

•00070 

40 

4-8 

4-65 

•00060 

50 

5-1 

4-95 

•00045 

60 

5-25 

5*25 

•00040 

70 

5-4 

5-5 

•00060 

80 

5-7 

5-8 

•00050 

90 

6-0 

6-0 

•00070 

100 

6-35 

6-35 

90 

Totals. 

•00505 

METHODS  AND  KESULTS   OF  TESTS  ON  MATERIALS  111 


Specimen  IY. — Wrought-Iron  Rod. 

Observations. 

Distance  between  gauge  marks  on  specimen,  8  inches. 
Leverage  of  machine,  22'4. 

Value  of  1  division  on  microscope  scale,  0*0002  inches. 
Diameter  of  specimen,  '381,  '389,  *385  inches. 
Mean  diameter,  *385  inches. 


Load. 

Lbs. 

Reading  on  Scale. 
(Loading.) 

Reading  on  Scale. 
(Unloading.) 

Extensions. 
Inches. 

10 

28 

28 

•0005 

20 

31 

30 

•0005 

30 

33 

33 

•0006 

40 

36 

36 

.0004 

50 

38 

38 

•0006 

60 

41 

41 

•0005 

70 

43-5 

43-o 

•0005 

80 

46 

46 

•0005 

90 

48-5 

48-5 

80 

Totals. 

•0041 

COLLECTED  BESULTS  OF  EXPERIMENT  TO  FIND  THE  VALUE  OF 
YOUNG'S  MODULUS. 


Specimen 
Number. 

Load    x 
Leverage. 

Area. 

Length. 

Exten- 
'  sion. 

Strain. 

Stress. 

E. 

Ibs. 

sq.  in. 

inches. 

inches. 

Ibs.  sq.  in. 

Ibs.  sq.  in. 

1       . 

1,904 

•Ill 

8 

•0094 

•00118 

17,190 

14-55  X  106 

2 

2,017 

•101 

8 

•0054 

•00063 

20,000 

29-4     X  106 

3     . 

2,017 

•no 

8 

.00505 

•00063 

18,310 

29-1     X  106 

4     . 

1,791 

•117 

8 

•0041 

•00051 

15,350 

30-1     X  106 

Determination  of  the  Modulus  of  Elasticity  by  Bending.— 

The  value  of  the  modulus  of  elasticity  can  also  be  obtained  by 
the  method  of  bending.  Suppose,  for  example,  it  is  required 
to  find  E,  for  a  wrought-iron  girder. 

The  testing  machine  is  arranged  so  that  the  girder  to  be 
tested  is  placed  across  the  knife-edges,  which  are  fixed  a  definite 
distance  apart.  The  load  is  then  applied  in  the  usual  way  to  the 
specimen  by  the  central  knife-edge,  the  maximum  deflection 
being  read  by  a  microscope  and  scale  affixed  to  the  girder. 


112 


A  HANDBOOK  OF  TESTING  MATERIALS 


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114 


A  HANDBOOK  OF  TESTING  MATERIALS 


A  succession  of  readings  are  taken  for  loads  varying  from 
zero  to  a  load  well  within  the  elastic  limit,  and  a  curve 
plotted  with  the  deflections  as  abscissae,  and  the  loads  as 
ordinates.  The  deflection  of  a  bar  supported  at  the  ends  and 
loaded  centrally  is  given  by  the  expression 

W/3 


y  =  Deflection. 

W  —  Load  applied. 

I    =  Distance  between  knife-edges. 

E  =  Modulus  of  elasticity. 

I    =  Moment  of  inertia  of  the  cross-section  of  the 

girder, 
from  which 


~7'48I 

I3 
~4ST  X  s^°Pe 


load-deflection  curve. 


The  cross-sectional  dimensions  of  the  girder  are  taken,  and 
the  moment  of  inertia  calculated.  A  simple  method  of 
obtaining  a  diagram  of  the  section  is  to  smear  the  latter  with 
red  lead,  and  obtain  an  impression  of  it  on  a  piece  of  paper. 

The  distance  between  the  knife-edges  is  known,  and  the 
slope  of  the  load-deflection  line  measured,  and  consequently 
E  can  be  calculated. 

Approximate  values  of  E  for  different  materials:  — 


Material. 

E. 

Lbs.  per  sq.  in.1 

Cast-iron 

17,000,000 

Wrought-iron  bars 

29,000,000 

Steel  boiler  plates  . 

30,000,000 

Steel  plate  (mild)     . 

31,000,000 

Cast-steel  (untempered)  . 
Copper  rolled  plate 

30,000,000 
15,000,000 

Brass       .... 

13,500,000 

Gun  -metal  or  bronze 

13,500,000 

Phosphor  bronze 

14,000,000 

Wood  (pine)    . 

1,600,000 

Wood  (oak)      .         ... 

1,450,000 

1  Unwin's  Machine  Design,  Part  I, 


METHODS  AND   EESULTS  OF   TESTS   OX  MATERIALS   115 

The  values  of  the  moduli  must  necessarily  depend  on  the 
qualities  of  the  materials,  so  that  the  values  given  above  must 
only  be  taken  as  approximate. 

Testing  with  the  Sphingometer. — As  explained  briefly  in 
Chapter  IV.,  page  66,  the  Sphingometer  can  be  used,  not 
only  to  determine  direct  extensions,  but  also  to  determine  the 
stress  distribution  in  the  specimen.  Normally  one  measures 
the  extension  in  three  planes  at  120°  and  the  mean  value  of 
these  three  measurements  is  used  for  the  calculation  of  E. 
The  Table  on  page  113  shows  how  the  readings  are  set  out  and 
calculated.  If  the  readings  of  each  strip  be  plotted  separately 
we  obtain  the  irregular  curves  shown  in  Fig.  71.  The  mean 
curve,  however,  in  the  case  of  an  elastic  specimen  is  straight. 
This  latter  line  gives  all  the  necessary  information  for 
obtaining  the  value  of  E,  etc.,  while  the  separate  curves  are 
used  to  determine  stress  distribution  in  the  manner  explained 
in  Appendix  III.,  page  249,  where  a  test  on  mild  steel  is 
worked  out.  The  readings  taken  in  three  planes  demonstrate 
that  the  load  does  not  pass  through  the  axis  of  the  specimen. 
It  is  especially  interesting  to  test  a  specimen,  and  obtain 
readings  with  the  instrument,  with  Yee-grips  in  the  testing 
machine. 


i  2 


CHAPTEK  VI 

TORSION    TESTING 

Brittle  Materials  in  Torsion.— When  brittle  materials, 
such  as  cast-iron,  are  subjected  to  torsion,  a  fracture,  usually 
almost  perfect  in  form,  results.  It  is  inclined  roughly,  at  an 
angle  of  45°  to  the  axis  of  the  specimen,  .and  makes  a 
complete  revolution  of  the  bar,  the  junction  of  the  ends  of  the 
spiral  being  approximately  a  straight  line.  The  theoretical 
line  of  fracture  is  illustrated  in  Fig.  72.  Fig.  73  shows  a 


r\ 


1 

1 

I    / 

v  —  ir 

v^ 

1 

f----> 

j 

i 

«/ 

FIG.  72. — Cast-iron  under  Torsion. 

drawing  of  a  hollow  specimen  fractured  in  torsion,  and  photo- 
graphs of  actual  fractures  are  shown  in  Plate  III.  It  can  be 
readily  seen  why  rupture  occurs  in  this  peculiar  way  if  an 
elementary  square  on  the  surface  of  the  specimen  be  con- 
sidered . 

The  torque  on  the  specimen  introduces  shear  forces  q 
(Fig.  72)  on  the  faces  of  the  elementary  square  as  shown.  But 
as  equilibrium  is  maintained,  it  is  evident  that  there  must  be 
equal  and  opposite  shear  forces  q  on  the  other  two  faces  It 
can  now  be  readily  proved  that  this  brings  into  action  a 
tensile  stress  of  equal  intensity  on  the  face  inclined  to  the 
others  at  45°. 

Now,  cast-iron  is  weaker  in  tension  than  in  compression  or 


TORSION  TESTING 


11' 


shear,  and  will  consequently  give  way  along  that  surface  where 
the  stress  is  tensile. 

If  this  tensile  stress  be  calculated,  it 
will  be  found  to  approximate  closely  to 
the  breaking  stress  found  by  pure 
tension.  The  calculation  is  performed 
as  follows  :— 

Twisting  moment  =  q  Z. 

Where  q  =  shear  stress  produced 
Z  =  modulus  of  the  section. 

But  Z  for  a  round  bar  —~YQ~ 
16XTM 


but  tensile  stress  ft—q 
16XTM 


The  following  results  were  obtained  from 
hollow  cast-iron  specimens  : — 


FIG.  73.  —  Fracture 
of  Cast  -  Iron 
Hollow  Specimen 
in  Torsion. 


No.  of 
Specimen. 

Internal 
Diameter. 

External 
Diameter. 

Torque.        ;  Tensile  Stress. 
Internal  Ibs.    Lbs.  persq.in. 

Angle  of 
Fracture. 
Internal. 

Angle  of 
Fracture. 
External. 

I 

1 

•904 

1-289 

6,020 

19,000 

45£° 

49i° 

2 

•892 

1-125 

2,920 

17,500 

45° 

49° 

3 

•990 

1-249 

3,180 

13,850 

47° 

45° 

Ductile  Materials. — The  behaviour  of  ductile  materials  in 
torsion  is  very  different  from  that  of  brittle  materials.  The 
specimen  twists  considerably  and  fracture,  being  due  to  shear, 
takes  place  in  a  plane  approximately  perpendicular  to  the  axis. 

Fig.  74  shows  a  load-strain  curve  plotted  for  mild  steel. 

As  the  angle  through  which  the  specimen  twists  is  large, 
it  can  be  obtained  sufficiently  accurately,  as  explained 
later1,  by  observing  the  number  of  turns  of  the  hand- 
wheel  actuating  the  torque.  Then,  knowing  the  number  of 
teeth  on  the  wheels  brought  into  play,  the  angle  of  twist  can 
1  See  description  of  the  Bailey  machine,  page  119. 


118 


A  HANDBOOK  OF  TESTING  MATERIALS 


be  calculated.  The  actual  readings  of  the  mercury  column 
are  plotted  as  ordinates.  Then  since  the  torque  arm  in  this 
case  is  4  inches  long,  the  torque  on  the  specimen  can  be 
obtained  by  multiplying  the  mercury  column  readings  by  four. 
It  will  be  observed  that  the  diagram  is  not  dissimilar  to 
those  obtained  from  tension  or  compression  tests.  There  is 
first  the  elastic  period,  giving  a  straight  line,  then  a  distinct 


TEST 

M/LO  STEEL  5P£C, 


650' 


FIG.  74. — Torsion  Test  on  Mild  Steel  (Autographic  Diagram). 

yield  point,  followed  by  a  curve  of  the  shape  usually  met  with 
in  autographic  diagrams.  Mild  steel  being  a  very  ductile 
material  twists  considerably  before  rupture,  and  the  curve 
shows  a  total  twist  of  1250  degrees. 

Wrought-iron  exhibits  the  same  characteristics,  though  not 
to  so  large  an  extent,  although  the  cracks  and  markings 
are  much  more  noticeable. 

Gunmetal  breaks  more  quickly,  the  surface  presenting  a 
a  very  uneven  and  blotched  appearance,  owing  to  the  effects 


TORSION  TESTING 


119 


of  compression  in  some  places  and  tension  in  others,  as  shown 
in  Fig.  75. 

Tests  on  cast-steel  show  that  its  behaviour  is  intermediate 
between  that  of  cast-iron  and  the  ductile  metals,  approaching 
more  nearly  to  either  extreme  according  as  the  steel  is  hard 

or  soft. 

TORSION  TESTING  MACHINES. 

The  "  Bailey  "  Torsion  Machine  (Fig.  76).— The  specimen 
consists  of  a  cylindrical  bar  with  enlarged  ends,  which  are 
either  of  square 
section  or  are  fitted 
into  square  caps  by 
means  of  keys.  The 
object  of  the  test  is 
to  find  the  resistance 
of  the  bar  to  torsion 
or  twisting,  so  that 
it  is  not  necessary 
to  grip  the  bar  tightly 
in  the  clips,  but  only 
to  prevent  it  from 
rotating  in  them.  In 
fact,  it  is  necessary 
to  allow  the  bar  to 
slide  a  little  longi- 
tudinally, as  when 
twisted  it  becomes 

rather  shorter  than  before.  Two  views  of  the  machine  are 
shown  in  Fig.  76.  The  end  AI  of  the  bar  is  twisted  by 
means  of  the  hand-wheel  B,  which  turns  the  worm-wheel  C. 
This  in  its  turn  rotates  the  spur-wheel  D,  to  which  the  grip  AI 
is  rigidly  attached.  The  other  end  of  the  bar,  held  in  the 
clip  A2,  attempts  to  turn  with  AI,  and  with  that  intent  pulls 
at  the  lever  E,  which  is  connected  by  the  tie  rod  Gr  to  the 
mercury  diaphragm1  F.  The  pressure  on  this  diaphragm 

1  In  the  usual  type  of  machine  this  diaphragm,  is  made  of  rubber- 
Prof.  Hummel  states  that  he  finds  a  great  improvement  by  substituting 
a  thin  brass  diaphragm  in  this  machine. 


PIG.  To. — Stresses  induced  in  a   Bar  sub- 
jected to  Pure  Torsion. 


120 


A  HANDBOOK  OF  TESTING  MATERIALS 


TORSION  TESTING  121 

causes  the  mercury  to  rise  in  a  column  H,  which  balances  the 
pressure  due  to  the  tie  rod  G.  Thus  the  height  of  the  column 
H  gives  a  measure  of  the  torque  or  twisting  force  exerted  on 
the  specimen.  The  mercury  column  is  calibrated  to  give  the 
tension  in  the  tie  road  G,  and,  since  the  length  of  the  arm  E 
is  known,  the  torque  on  the  specimen  is  easily  found. 

"Thurston"  Torsion  Machine. — In  this  machine  the  load  is 
applied  in  the  same  way,  but  the  method  of  measurement  is 
different.  A  pendulum  weight  is  'affixed  to  the  free  end  of 
the  test  bar,  and,  as  the  load  is  applied,  the  test  bar  is  able 
to  move  this  pendulum  through  a  distance  proportional  to  the 
load.  The  pendulum,  therefore,  is  caused  to  move  a  pointer 
along  its  quadrant,  the  latter  being  calibrated  to  read  the  load 
on  the  specimen.  When  the  bar  breaks,  the  pendulum  swings 
back  into  a  vertical  position,  but  the  pointer  remains  in  the 
position  that  it  had  assumed  just  before  the  specimen  broke. 
The  final  position  of  the  pointer,  then,  gives  us  the  breaking 
torque  on  the  test  bar. 

"Avery"  Torsion  Machine. — The  Avery  machine  also  has 
its  load  applied  in  the  same  manner  as  the  Bailey  and 
Thurston  machines,  viz.,  by  a  worm  and  worm-wheel,  but, 
again,  the  method  of  measurement  is  different.  The  stress  is 
indicated  by  means  of  a  system  of  weighing  levers,  similar  to 
those  in  the  Kiehle  testing  machine,  being  finally  measured 
by  running  out  a  poise  along  a  graduated  steelyard.  In  the 
15,000-inch  Ib.  machine  there  are  three  of  these  poises,  each 
weighing  60  Ibs.  The  first  indicates  up  to  5,000  inch  Ibs., 
when  each  scale  division  on  the  steelyard  represents  J  Ib. 
When  two  poises  are  coupled  together  readings  can  be  taken 
up  to  10,000  inch  Ibs.,  and  when  the  whole  180  Ibs.  are  run 
along  the  scale  they  give  a  total  capacity  of  15,000  inch  Ibs., 
with  readings  of  5  inch  Ibs.  per  scale  division.  A  vertical 
scale  is  sometimes  fixed  on  the  front  end  of  the  steelyard, 
and  a  telescope  to  the  frame  of  the  machine.  By  this  means 
we  can  adjust  the  lever  with  great  accuracy  until  it  rests 
in  a  perfectly  horizontal  position.  This  machine  will  take 
square  bars  up  to  J  inch  side,  or  rectangular  specimens  up 


122  A  HANDBOOK  OF  TESTING  MATERIALS 

to  a  maximum  size  of  1  inch  X  f  inch.  The  bracket  on 
which  the  straining  gear  is  fixed  is  capable  of  movement  to 
admit  specimens  of  a  maximum  length  of  15  inches.  The 
shortening  of  the  specimen  under  the  torsional  load  is  provided 
for  by  the  insertion  of  hardened  steel  rollers.  The  actual 
strain  on  the  specimen  is  observed  by  fastening  indicating 
arms  to  its  two  ends  a  gauge  length  apart.  These  arms  are 
in  line  with  each  other  at  the  start,  but  as  the. load  is  applied 
one  end  gets  twisted  more*  than  the  other,  so  that  the  angle 
between  them  at  a  definite  load  gives  us  the  torsional  strain 
at  that  load. 

This  machine  is  also  arranged  to  measure  a  torsional  stress 
applied  in  the  reverse  direction.  The  main  torsion  lever  T  is 
keyed  on  a  sleeve  which  is  free  to  revolve  in  ball  bearings. 
An  intermediate  lever  E  is  arranged  within  this  main  lever, 
and  is  pivoted  at  a  point  G  between  the  axis  of  the  specimen 
and  that  of  the  tension  rod  which  transmits  the  stress  to  the 
steelyard.  When  the  torsion  is  applied  in  a  clockwise  direc- 
tion, the  knife-edge  C  of  the  main  lever  pulls  up  the  left  hand 
end  of  the  intermediate  lever,  and  so  depresses  the  end  that  is 
attached  to  the  tension  rod.  When  the  stress  is  applied  in  a 
contra-clockwise  direction,  the  knife-edge  K  raises  the  point 
E  of  the  intermediate  lever,  and  again  pulls  the  tension  rod 
downward.  So  that,  in  whatever  direction  the  torsional  load 
is  exerted,  the  short  end  of  the  steelyard  is  always  pulled 
downward,  balance  being  restored  by  running  the  poise  along 
the  arm.  The  leverages  are  so  arranged  that  the  load  on  the 
specimen,  in  either  direction,  can  be  read  directly  on  the 
same  scale. 

The  same  makers  also  manufacture  a  testing  machine  to 
give  results  in  tension  and  torsion  simultaneously,  so  that 
the  effect  of  the  combined  stresses  can  be  read  off  in  one 
machine.  It  consists  practically  of  a  hydraulic  tension 
machine  and  a  hand-power  torsion  machine  on  the  same 
bedplate.  The  principles  upon  which  the  combined  machines 
act  are  similar  to  those  already  given  for  the  separate 
machines.  A  detailed  account  of  the  tension-torsion  tester 


TORSION  TESTING 


123 


Tension  Rod- 


ft 


®\ 


Fig.  77. — Hand-Torsion  Testing  Machine. 


124 


A  HANDBOOK  OF  TESTING  MATERIALS 


is  given  on  page  251.  The  two  steelyards,  one  for  each  kind  of 
stress,  are  placed  so  that  neither  interferes  with  the  working 
of  the  other,  but  are  near  enough  together  to  enable  the 
readings  to  be  taken  by  one  man. 

The  Torsion  Sphingometer. — The  principle  of  the  twisted 
strip  has  been  applied  to  the  instrument  which  is  used  for 
recording  torsion  strains.  To  each  of  the  carriers  "  C ': 
(Fig.  40)  is  fastened  an  arm  carrying  a  "  V "  block.  The 
sphingometer  tube  is  now  placed  at  right  angles  to  the  axis  of 
the  specimen.  A  45°  mirror  is  placed  vertically  under  the 
mirror  of  the  sphingometer  strip,  and  is  so  hinged  that  it  will 
move  in  two  planes.  This  latter  arrangement  makes  it  easy  to 

arrange  for  illumi- 
nating  both 
mirrors.  Any  move- 
ment of  the  carriers 
"C"due  to  a  torque 
will  cause  the 
sphingometer  strip 
to  extend.  This 
extension  is  magni- 
fied and  recorded 
in  the  usual 

manner.  The  method  of  calibration  is  by  using  a  gauge 
to  measure  the  perpendicular  distance  of  the  strip  from 
the  circumference  of  the  specimen.  Then  since  the  specimen 
is  circular,  the  distance  of  the  centre  of  the  strip  from  the 
centre  of  the  specimen  is  also  known.  The  proof  of  this  is  as 
follows :  Let  B  C  (Fig.  78)  represent  the  strip  of  length  Z,  and 
let  A  be  the  centre  of  the  specimen.  Then  from  the  figure  we 
have  /2i=c2+Z>2— 2fcc  cos  A.  Whence  2Z<M=26c  sin  AdA.  But 


FIG.  78. — Diagram  of  Torsion  Meter. 


Ic  sin  A =2  X  area  of  triangle  =pl.     . ' .  dl——dA. 

Hence  it  is  obvious  that  in  order  to  measure  the  angular 
displacement  the  only  necessary  measurement  is  that  of  the 
perpendicular  to  the  strip  from  the  centre  of  specimen.  This 
can  be  obtained  very  accurately  by  means  of  a  gauge.  In 


TORSION  TESTING 


125 


Fig.  40  the  three  strips  used  for  measuring  strains  in  a 
tension  or  compression  test  are  shown,  and  also  the  torsion 
strip  is  in  position.  It  may  be  mentioned  that  the  position  of 
this  strip  can  be  readily  altered  if  it  is  desired  to  use  short 
distances  between  the  gauge-points.  Lever  arms  may  be 
fastened  to  both  carriers,  and  the  torsion  Y-block  secured  to 
the  lever  arms.  This  also  increases  the  sensitiveness  of  the 
strip.  It  has  the  further  advantage  that  the  perpendicular 
distance  p  is  measured  with  greater  accuracy.  A  torsion  test 


«j    IZi 

I 

m 


TORSION  TESTS  HC4'  b  C,  AND cf 

A.  Primary  Test 

B.  Affer  overstraining 

C .  ft ffer  fur/her  oi/ersframing 
Torque  arm  -  J82 /nc/ies 


Tw/sr 
FIG.  79. — Effect  of  Overstrain  in  Torsion  (Mild  Steel  Specimen). 

and  the  curve  obtained  with  a  copper  specimen  is  given  above. 
For  a  description  of  a  very  excellent  torsionmeter,  devised 
by  Prof.  Coker,  see  page  258. 

Typical  Results  of  Torsion  Tests. — In  Fig.  74  we  showed 
a  typical  curve  for  a  torsion  test  when  carried  up  to  fracture, 
but  many  of  the  most  interesting  torsion  experiments  are  per- 
formed with  stresses  which  only  slightly  exceed  the  elastic 
limit. 

Effect  of  Overstrain. — On  page  103  a  brief  explanation  of 
this  phenomenon  was  given  as  it  appears  in  the  case  of  tension 
and  compression  specimens.  Figs.  79  to  83  illustrate  the 


126 


A  HANDBOOK  OF  TESTING  MATEKIALS 


TOJOfOUt  TESTS  SSS  e  fff  A 
e  -  /Ifler  lOm'tiurcs  at  /OO'C 
f-    After  overs  framing 
ff     After  further  overstraining 
ri     Aftf-  furtfies  overstraining 


TW/ST 
PIG.  80. — Effect  of  Overstrain  on  Mild  Steel  in  Torsion. 

effect  in  the  case  of  mild  steel  torsion  specimens,  together 
with  the  allied  effect  of  low  heat  treatment.  All  the  dia- 
grams given  in  this  section  were  obtained  with  the  torsion 
sphingometer  described  on  page  124.  Fig.  84  shows  yet 


5>2cirpen  ADI. 

TORSlOn  TfcST 


A...  Primara  fesf. 

B . . .  After  10  mSofcS  aT  lOcTC 

C...  Imrpe&iafelg  afferD. 

...4daQ3  after  C. 
£_..  ImnTcSiofelu  after D. 
fr.....  After  10  mirufea  ar 


FIG.  81. — Effect  of  Time  and  Boiling  on  Mild  Steel. 


TOESIOX   TESTING 


127 


TORSION  TESTS  SSff  ct.e./itHi  t 
d-  Primary  Test 
e  -  Mer  10  minutes  at  100'C 
h  -  After  raising  elastic  limit  by  overstrain 
I  -  AHer  10  minules  at  100'C 


Tw/sr 


FIG.  82. ---Effect  of  Overstrain  and  Boiling  on  Mild  Steel  in  Torsion. 


Specimen  35? 

TOR5IOrtT£5T. 


D... 

C...A(IerlOrr?ir?aar  100"  C 


PIG.  83.— Effect  of  Overstrain  and  Boiling  on  Mild  Steel  in  Torsion. 


128 


A  HANDBOOK  OF  TESTING  MATERIALS 


another  phenomenon  in  connection  with  the  elastic  break- 
down of  materials.  If  after  passing  the  elastic  limit  the  load 
be  sustained  constant  for  some  time,  the  twist  will  be  found 
to  increase.  In  Fig.  84  the  time  of  taking  the  different 
readings  is  placed  in  juxtaposition  with  the  plotted  point.  It 


TORSION  TEST  ALIa 
Torque  arm  -  38  2  inches 


TW/ST 
FIG.  84. — Pure  Torsion  Test  on  Aluminium  showing  Time  Effect. 

will  be  seen  that  at  first  the  "  slip  "  is  very  small  even  over  a 
considerable  time,  while  the  effect  becomes  gradually  more 
marked  until  complete  breakdown  occurs.  A  full  discussion 
of  this  gradual  breakdown  will  be  found  in  a  paper  read  by 
the  author  before  the  Iron  and  Steel  Institute.1 

Fig.  85  shows  the  effect  of  boiling  in  water  on  the  recovery 
of  elastic  properties  in  the  case  of  aluminium. 

1  "  The  Elastic  Breakdown  of  Certain  Steels,"  Journal  of  the  Iron  and 
Steel  Institute,  May,  1910. 


TOESION  TESTING 


129 


eol 


TORS/ON  TESTS  AL4  6w 
C-  After  /O  minuses  at  /OO°C 


Torque  arm  =  38  2  inches. 


TW/ST 
FIG.  85. — Torsion  Tests  on  Aluminium. 

Figs.  86  and  87,  on  copper  specimens,  will  show  that 
normal  annealed  high  conductivity  copper  has  no  very 
marked  elastic  limit,  the  curve  gradually  bending  over. 


TORS/ON  TESTS  HCJ'a  AND  HC4'a 


Tw/sr 
FIG.  86. — Torsion  Tests  on  Copper. 


T.M. 


130 


A  HANDBOOK  OF  TESTING  MATERIALS 


roffs/ott  rtsrs  Hcs'donde 

/*   Primary  Tetf 
A  After  overstraining 
Torque  arm  *  J8Z /acfes 


TWIST 


FIG.  87. — Effect  of  Overstrain  on  Copper. 

After  overstraining  beyond  the  elastic  limit,  a  hardening 
effect  takes  place,  which  causes  the  material  to  give  a  curve 
more  closely  allied  to  other  materials.  The  curve  obtained 


TORS /ON  TESTS  MS  a **o  b 
a  Primary  Test 
b  /mmediate/y  offer    ~ 


Tw/sr 

FIG.  88.— Torsion  Tests  on  Muntz  Metal. 

with  the  primary  test  in  Fig.  87  is  the  one  starting  from  a 
point  farthest  to  the  left. 

Table  IV.  and  the  curves  in  Fig.  88  show  the  arrangement 
of  a  test  on  Muntz  metal. 


TOESION  TESTING 


131 


TORS/ON   TESTS  MS  b  *HD  C 

C  after  /O  minufes  af  /00°C 


Tw/sr 
FIG.  89. — Torsion  Tests  on  Muntz  Metal. 


TABLE  IV.— TORSIOX  TEST  ON  Muxrz  METAL  (M5a). 
(FOE,  CURVES,  SEE  FIG,  88.) 

Diameter  of  specimen  =  1*000  inch. 

Perpendicular  distance  of  strip  from  centre  of  specimen  =  3*72  inches. 

Calibration  of  strip,  1  scale  division  =  0'00010800  inch. 


Load  in 
Ibs. 

Scale 
Readings. 

Scale 
Differences. 

T*n  of  a 
Radian. 

20 

-193 

0 

40 

—66 

127 

0-368 

50 

2 

191 

0-554 

60 

+61 

254 

0-737 

70 

+  125 

318 

0-923 

80 

+  193 

386 

1-120 

85 

+228 

421 

1-220 

90 

+265 

458 

1-330 

90 

-30 

Inst*.  reset. 

— 

95 

+  10 

498 

1-445 

100 

+53 

541 

1-570 

105 

+  100 

588 

1-707 

110 

+  152 

640 

1-857 

115 

+215 

703 

2-040 

On  examining  curve  SSa,  it  will  be  seen  that  the  curve 
ceases  to  be  straight  where  load  is  85  Ibs.,  whence  for  the 
shear  stress  at  elastic  limit,  the  moment  of  the  couple 

K  2 


132 


A  HANDBOOK  OF  TESTING  MATERIALS 


is  TxL  (in  test  M5a,  T— 85   Ibs.  and   L=38'2  inches)  we 

i  ft 
have  rr:=TLx— FO,  where  q  is  maximum  shear  stress. 

ml3 

85  X  38-2  X  16 


Whence  q  = 


7T    X    13 


=  16550  Ibs.  per  square  inch. 
/(? 

-1 >- 


FIG.  90. — Kectangular  Block  under  Shear  Stress. 

The  curve  S8b  is  a  test  on  the  same  specimen  immediately 
after  test  M5#,  plotted  in  Fig.  88«. 

Fig.  89  shows  the  effect  of  overstrain  and  subsequent  boiling 
on  Muntz  metal. 


FIG.  91. — Circular  Specimen  in  Torsion. 

Modulus    of    Rigidity    C. — The    modulus    of    rigidity    C 
_ shear  stress  in  Ibs.  per  sq.  in._^ 
~  shear  strain  per  inch  length  ~~  5 ' 

5  is  the  strain  between  two  planes  an  inch  apart  (Fig.  90). 

The  simplest  method  of  finding  C  for  any  material  is  by 
applying  a  torque  to  a  round  specimen  and  observing  the 
angle  oi  twist  over  a  definite  gauge  length.  This  is  quite 


TOKSION  TESTING  133 

easily  done  in  the  Bailey  machine,  a  torsionometer  being  used 
to  measure  the  angle  of  twist.  A  succession  of  readings  of 
twisting  moment  and  angle  of  twist  are  thus  obtained,  both 
for  ascending  and  descending  values  of  the  twisting  moment, 
and  a  curve  plotted  with  the  angles  of  twist  as  abscissae,  and 
the  twisting  moments  as  ordinates.  Careful  measurements 
are  also  made  of  the  diameter  of  the  specimen  and  the  gauge 
length. 

Let  Fig.  91  represent  the  specimen  of  gauge  length  L, 
and  the  radius  r. 

Let  $  =  angle  of  strain  in  circular  measure,  and  9  = 
angle  of  twist  in  circular  measure. 

Then  C=|        ...  (1) 

where  q  —  shear  stress  produced.  But  twisting  moment, 
TM  =  q  Z. 

where  Z  —  polar  modulus  of  the  section. 

TM 

.  * .  o  =       . 
/^ 

And  since  0,  not  <f>,  is  measured  by  the  torsionometer, 

_r0 

Substitute  in  (1) 

,    TM    L     L 

.  *.  C  ^--^-X-^^-x  slope  of  stress-strain  curve. 

All  these  quantities  are  known,  and  consequently  C  can  be 
calculated. 

Approximate  values  of  C  for  different  materials. 


Material. 


C. 

Lbs.  per  sq.  in. 


Cast-iron 6,300,000 

Wrought-iron  bars      .         .         .  10,500,000 

Steel  boiler  plate          .         .         .  13,500,000 

Cast  steel  (untempered)       .         .  12,000,000 

Copper  rolled  plate      .         .         .  5,600,000 

Phosphor  bronze          .         •         .  I            5,250,000 


134 


A  HANDBOOK  OF  TESTING  MATEEIALS 


Poisson's  Ratio.— When  a  specimen  is  loaded,  there  is  a 
direct  strain — tensile  or  compressive,  according  to  the  nature 


FIG.  92. -.-Apparatus  for  Torsion  Experiments  on  Wires. 

of    the    test — and    also   a   lateral    strain,    the    sign   of  this 
strain  heing  the  reverse  of  the  direct  one. 

The  ratio  of  the  direct  strain  to  lateral  strain  is  known  as 
Poisson's  Eatio,  and  is  usually  designated  by  the  letter  in. 
As  the  lateral  strain  is  very  small,  it  is  exceedingly  difficult  to 


TOESION  TESTING  135 

measure  it  accurately  by  direct  method.  Hence  the  most 
usual  way  is  to  obtain  the  moduli  of  elasticity  and  rigidity  in 
the  manner  already  stated,  and  calculate  m  from  the  following 
equation  : — 

m=E-2C 

The  following  table  gives  mean  values  of  m  for  some  of 
the  more  usual  metals  : — 


Metal. 


Cast-iron 

Wrought-iron 

Steel 


3-7 
3-6 
3-25 


Brass 3-0 

Copper         .         .         .         .         .  j  2'6 


Torsional  Experiments  on  Wire. — The  value  of  the  shear 
modulus  can  be  determined  in  the  case  of  wires  by  two  methods 
— (a)  by  static  deflection  and  (b)  by  torsion  vibration.  Fig.  92 
shows  the  first  method  in  diagrammatic  outline.  A  wire  is  first 
pulled  taut  by  being  fixed  at  its  lower  end  and  attached  to  a 
tightening  screw  at  the  top.  To  the  wire  is  attached  a  light 
brass  drum  carrying  a  scale  divided  in  degrees.  A  light  cord 
is  passed  once  or  twice  round  the  drum  and  over  two  fixed 
pulleys.  To  the  ends  of  the  cords  are  attached  small  scale 
pans  or  weight  hooks.  Equal  weights  are  placed  in  the  scale 
pans,  and  the  twist  of  the  wire  observed  by  reading  the  move- 
ment of  the  circular  scale  relative  to  a  fixed  pointer.  The 
twisting  movement  is,  of  course,  the  product  of  the  weight  in 
one  scale  pan  into  the  diameter  of  the  drum.  C  is  obtained 
from  the  formula — 

n_oS4M/, 
W 

where  M  is  the  twisting  movement  in  Ibs.  inches,  I  the  length 
of  wire  in  inches,  0  the  deflection  in  degrees,  and  d  the 
diameter  of  the  wire. 


136 


A  HANDBOOK  OF  TESTING  MATEEIALS 


Fig.  93  shows  the  very  simple  form  of  apparatus  used  to 
determine  C  by  torsional  vibrations.  The  wire  is  fixed  as 
before,  and  carries  near  its  lower  extremity  a  light  brass  tube. 
Four  other  pieces  of  tube  are  provided,  each  exactly  one  quarter 

of  the  length  of  the  long 
tube,  and  made  to  slip 
inside  it.  Two  of  the 
short  pieces  are  filled 
with  lead,  and  two  are 
empty.  Two  values  of 
the  time  of  torsional 
vibration  are  obtained— 
one  when  the  two  empty 
tubes  are  at  the  extremity 
of  the  long  tube,  and 
the  other  when  this 
order  is  reversed  and  the 
loaded  tubes  are  at  the 
extremities  and  the  empty 
ones  at  the  centre.  It 
can  be  shown  that 


D 


FIG.  93. — Apparatus  for  Testing  Torsional 
Vibrations  of  Wires. 


Where  C  is  modulus 
of  torsional  rigidity. 

I  is  length  of  wire  in 
inches. 

d  diameter  of  wire  in 
inches. 


mi  mass  of  each  of  the  tubes  filled  with  lead  in  Ibs. 
w2  mass  of  each  of  the  empty  brass  tubes  in  Ibs. 
x  half  the  length  of  the  long  tube. 

ti  and  t%  the  observed  times  of  torsional  vibrations,  with 
loaded  tubes  outside  and  inside  respectively. 


CHAPTEE  VII 

IMPACT    AND    HARDNESS    TESTS 

THE  object  of  an  impact  test  is  to  obtain  the  efficiency  of 
the  material  on  test,  when  it  has  to  be  introduced  into  a 
machine  or  structure  where  it  will  be  subjected  to  shocks  or 
suddenly  applied  loads. 

The  importance  of  this  branch  of  testing  work  is  well 
illustrated  in  a  paper  on  "  Impact  Tests  "  read  before  the 
Institute  of  Mechanical  Engineers  in  1904  03^  Messrs.  Seaton 
and  Jude,  where  an  approximate  analysis  of  the  stresses  to 
which  the  steel  parts  of  a  reciprocating  steam  engine  is 
given  as  follows: — 

Constant  tension      ....  3*91  per  cent. 
Constant  tension  and  compression 

(range  from  0  to  a  maximum)     .  1-80       „ 

Constant  tension  and  shock     .         .  48'80       „ 
Alternating  tension  and  compression 

with  shock 2*81       „ 

Kepeat  tension  (from  a  constant  to 

a  maximum)  with  shock       .         .  36'00       ,, 

Miscellaneous  and  doubtful  I'll 


Total  .  100-00 


"It  will  therefore  be  seen  that  87'6  per  cent,  of  the  whole 
of  the  engine's  stresses  are  more  or  less  due  to  shock,  whilst 
pure  tension  stresses  form  an  insignificant  percentage  of  the 
total  stress."  It  is  furthermore  stated  that  if  other  machines 
were  analysed  in  a  similar  manner,  nine  out  of  ten  would  be 
found  to  be  working  under  similar  conditions. 

AYery  Machine. — The  machine  consists  of  two  A  frames  of 


138  A  HANDBOOK  OF  TESTING  MATEEIALS 

cast-iron,  between  which  swings  a  pendulum  consisting  of  a 
steel  tube,  terminating  in  a  cast-iron  head.  The  specimen, 
consisting  of  a  small  piece  of  metal  f  of  an  inch  wide  and 
T36-  inch  in  thickness,  is  placed  in  a  vertical  position  in  a  vice 
at  the  base  of  the  instrument.  The  pendulum  is  then  raised" 
to  the  required  height  and  secured  by  the  releasing  trigger 
carried  on  the  curved  arm  of  the  frame.  The  height  to  which 
the  pendulum  is  raised,  and  consequently  its  potential  energy, 
is  indicated  by  a  pointer  on  the  quadrant  at  the  top  of  the 
frame.  When  the  trigger  is  released,  allowing  the  pendulum 
to  fall  and  strike  the  specimen,  the  indicating  pointer  engages 
with  a  loose  registering  finger,  and  carries  the  latter  forward 
with  it.  Now  if  no  specimen  were  present,  the  pendulum 
would  rise  to  an  equal  height  on  the  other  side,  no  energy 
being  absorbed.  But  when  a  specimen  is  broken,  the  pendulum 
does  not  rise  so  high ;  its  travel  on  the  other  side  of  the 
vertical,  being  inversely  proportional  to  the  amount  of  work 
done  in  breaking  the  specimen.  Hence  the  loose  registering 
finger  is  carried  over  to  the  farthest  point  reached  by  the 
pendulum  after  breaking  the  specimen,  and  stays  there,  thus 
indicating  directly  the  amount  of  work  done  in  breaking  the 
test  piece.  The  maximum  capacity  of  this  machine  is  23 
ft.  Ibs. 

Tensile  Impact  Tester. — The  following  is  a  simple  machine 
for  examining  the  properties  of  materials  under  tensile  impact. 
The  specimen,  consisting,  let  us  say,  of  a  long  piece  of  steel 
wire,  is  gripped  at  the  upper  end  in  a  block  which  slides  upon 
two  or  four  vertical  pillars.  The  lower  end  is  attached  to  a 
heavy  hammer-block  which  keeps  the  specimen  or  wire  in 
tension.  The  whole  system  is  hoisted  to  some  known  height 
up  the  vertical  pillars,  and  then  allowed  to  fall.  In  falling, 
the  block  which  holds  the  top  end  of  the  specimen  is  suddenly 
arrested  by  a  stop,  fixed  to  the  supporting  pillars,  while  the 
hammer-block  at  the  lower  end  is  still  unsupported.  The 
energy  contained  in  the  hammer  is  arranged  to  be  more  than 
sufficient  to  rupture  the  test  bar  or  wire.  The  actual  energy 
required  to  just  break  the  specimen  is  obtained  as  follows. 


IMPACT  AND  HARDNESS  TESTS 


139 


60 

ma 


& 


140  A  HANDBOOK  OF  TESTING  MATEEIALS 

A  rotating  drum  is  provided,  and  the  hammer  has  a  pencil 
attached  to  it,  which,  on  falling,  describes  a  time-displace- 
ment curve.  The  surface  speed  of  the  drum  is  found  by 
holding  against  it  a  vibrating  tuning  fork,  which  has  a 
known  period.  This  being  known,  the  velocity  of  the  hammer 
at  any  point  in  the  descent  can  be  obtained  from  this  curve. 
We  can  therefore  find  the  energy  contained  in  the  hammer 
at  the  time  of  rupture  by  computing  the  velocity  just  after 
the  moment  of  rupture.  We  can  obtain  the  total  energy  in 
the  hammer  at  the  start  from  the  height  of  fall,  and  therefore, 
by  subtraction,  we  can  find  the  energy  required  to  break  the 
specimen. 

A  machine  of  identically  the  same  principle,  but  some- 
what different  in  detail,  has  been  recently  described  in  a 
paper  before  the  Institution  of  Mechanical  Engineers  by 
Messrs.  Blount,  Kirkaldy,  and  Sankey.1  This  machine,  which 
is  constructed  for  breaking  specimens  of  mild  steel  0'357  inch 
diameter,  is  arranged  in  a  building  so  as  to  have  an  available 
fall  of  forty  feet.  The  anvil  is  of  an  exceptionally  rigid 
and  heavy  design  consisting  of  two  castings,  each  weighing 
400  Ibs.,  securely  bolted  to  the  top  of  four  rolled  steel  joists, 
which  in  turn  are  bedded  in  concrete.  The  effective  weight 
is  2,000  Ibs.  The  test  piece  connects  together  the  "tup" 
and  arresting  cross-head,  and  the  whole  is  allowed  to  fall 
freely  until  the  arresting  piece  strikes  the  anvil,  when  the 
specimen  is  broken  and  the  tup  continues  to  fall.  The  tup 
can  be  varied  in  weight  2  Ibs.  at  a  time  between  10  Ibs.  and 
20  Ibs.  Electric  contacts  are  broken  by  the  falling  weight 
(1)  at  the  moment  of  release,  (2)  on  striking  the  anvil,  and 
(3)  after  the  tup  has  fallen  10  feet  after  fracture  of  speci- 
men. By  means  of  a  Morse  telegraph  "  inker,"  a  pendulum 
half-second  contact  maker,  and  a  vibrating  tuning  fork,  the 
making  and  breaking  of  the  electric  contacts  works  the  usual 
cronographic  method,  so  that  the  times  between  the  standard 
points  given  above  can  be  ascertained  to  within  about  "005. 

1  "  Comparison  of  the  Tensile,  Impact-Tensile,  and  Repeated-Bendin 
Methods  of  Testing  Steel."  Proc.  Inst.  Mech.  Eng.,  May  27th,  1910. 


IMPACT  AND  HAEDNESS  TESTS  141 

The  time  between  points  (1)  and  (2)  merely  serves  as  a  check, 
while  the  time  between  (2)  and  (3)  serves  to  calculate  the 
energy  remaining  in  the  tup  after  fracture  of  the  specimen. 
The  full  expression  for  the  energy  of  breaking  is 

Energy  absorbed  ==  W  |  H-i(|-f 

where  H  is  the  height  of  free  fall  before  striking  anvil ; 

h   is  the  height  of  free  fall  after  striking  anvil,  i.e., 
between  the  anvil  contact  and  the  bottom  contact ; 

W  is  the  weight  of  the  tup  ;  and 

t    is  the  time-interval  between  the  anvil  and  bottom 

contact. 

It  was  found  by  the  experimenters  previously  mentioned 
that  the  energy  absorbed  per  cubic  inch  in  an  impact  tensile 
test,  divided  by  the  elongation,  gave  a  measure  of  the  breaking 
stress  in  an  ordinary  tensile  static  test.  The  strength  given 
by  the  impact  test  averaged  about  1*2  times  that  given  in  a 
static  test.  It  is  worth  noting  that  the  authors  of  the  above 
mentioned  papers  say,  "  The  energy  absorbed  per  cubic  inch 
does  not  vary  greatly  with  the  various  types  of  steel ;  it  is 
approximately  50  per  cent,  more  than  that  obtained  by  the 
static  tensile  test,  and  is  also  no  definite  criterion  of  the  type 
of  steel." 

National  Physical  Laboratory  Apparatus.1 — The  machine 
consists  of  a  cast-iron  anvil  and  a  tup,  each  supported  by 
four  pieces  of  steel  strip  £  inch  wide  by  -£§  inch  thick  and 
about  12  feet  long.  The  anvil  has  two  heavy  bosses  on  the 
sides,  through  which  passes  two  pieces  of  round  steel  bar. 
These  can  be  adjusted  to  protrude  any  distance  towards  the 
middle  of  the  anvil,  and  are  locked  by  means  of  set-screws. 
The  ends  of  these  bars  are  cut  away  to  hold  the  knife- 
edges,  against  which  rests  the  specimen,  kept  at  the  right 
height  by  adjustable  supports.  The  tup  is  provided  with 
a  steel  knife-edge,  adjustable  outwards  so  as  to  just  touch 
the  specimen  when  the  tup  and  the  anvil  are  at  rest. 

1  Described  in  Proc.  Inst.  Mech.  Eng.,  1905,  p.  886. 


142 


A  HANDBOOK  OF  TESTING  MATEEIALS 


From  the  back  of  both  tup  and  anvil  a  string  is  carried 
over  a  pulley  near  the  roof,  with  a  small  weight  attached 
(just  sufficient  to  keep  the  string  taut).  The  rise  of  these 
weights  is  a  measure  of  the  height  through  which  the  tup 
or  anvil  is  raised.  The  actual  heights  of  the  tup  and  anvil 
corresponding  to  the  observed  motions  of  the  small  weights 
on  the  strings  is  obtained  by  separate  experiment. 

The  anvil  weighs  about  60  Ibs.  and  the  tup  about  47  Ibs. 
The  specimens  used  in  these  tests  were  5  inches  long  by 
f  inch  square,  and  were  notched  on  the  tension  side  with  a 
small  V  groove.  The  knife-edges  were  placed  4^  inches 
apart.  The  method  of  test  is  as  follows : — The  specimen 
is  placed  in  the  anvil,  and  the  tup  tied  back  at  the  desired 
height  by  a  piece  of  thin  string.  The  tup  is  then  released 
by  severing  the  string  with  a  sharp  knife,  and  an  observer 
notes  the  height  to  which  the  anvil  is  forced,  while  a  second 

TABLE  Y. — NICKEL  ALLOYS  FORGED  AND  COOLED  FROM  800°  C. 
(1,472°  P.). 


Shock  Tests. 

Hardness  Tests. 

Ni. 
Alloy. 

Fall  of 
46-7  Ibs. 
Hammer. 

Energy 
Absorbed. 

Bending 
Angle. 

Indentation  in  l5\T?f 
inch  (Unwin's  Test). 

BrineU's 
Ball  Test. 
Hardness 
Number. 

Relative 
Hardness. 
Indenta- 
tion 
Method. 
Swedish 

Load 

Load 

1-5  tons. 

2  -5  tons. 

Iron  =  1. 

Inches. 

Inch  Ibs. 

Degrees. 

A 

13-23 

451 

18-0 

7-2 

15-0 

202 

1-6 

B 

13-05 

428 

17-0 

6-4 

14'5 

207 

1-8 

C 

13-67 

454 

16-5 

7-0 

19-5 

212 

1-6 

D 

13-92 

460 

15-5 

6-0 

12-3 

217 

1-5 

E 

13-67 

217 

Broken 

4-2 

8-7 

321 

— 

O. 

F 

13-67 

105 

Broken 

2-5 

5-5 

532 

— 

, 

O. 

G 

14-15 

230 

Broken 

2-5 

5-7 

578 

2-2 

O. 

H 

14-17 

436 

7*5 

3-2 

6-2 

555 

2-2 

J 

13-33 

432 

14-5 

5-0 

10.3 

293 

2-0 

K 

13-77 

452 

28-0 

16 

40 

131 

1*2 

IMPACT  AND  HABDNESS  TESTS 


143 


observer  notes  the  height  to  which  the  tup  swings  after 
the  blow. 

The  work  given  as  that  required  to  deform  or  break  the 
specimen  is  the  difference  between  the  kinetic  energy  of  the 
system  before  and  after  the  blow,  calculated  from  the  heights 
to  which  the  masses  are  raised. 

The  preceding  table  from  the  Seventh  Keport  of  the  Alloys 
Eesearch  Committee l  shows  some  results  obtained  on  the 
nickel  alloys  described  in  that  paper. 

For  purpose  of  comparison  hardness  tests  taken  by  means 
of  (a)  penetration  of  a  hardened  steel  point,  (b)  Unwin's  tests, 
(c)  Brinell's  ball  test  (see  page  147),  are  given  below. 


FIG.  95. — Impact  Testing  Machine,  repeated  Hammer  Blows. 

Seaton  and  Jude's  Impact  Testing  Machine.— This  is  a 

simple  machine  and  consists  merely  in  arranging  a  weight 
attached  to  guides  and  arranged  to  fall  through  a  definite 
distance  on  to  a  notched  specimen  held  in  a  fixed  anvil.  A 
very  usual  size  of  specimen  is  4  inches  X  J  inch  x  J  inch  with 
a  notch  about  J  inch  deep  in  the  centre.  This  is  held  in  the 
anvil  so  as  to  form  a  beam  supported  at  the  ends  with  about 
3  inches  span.  The  total  falling  weight  is  about  7  Ibs.,  and 
is  arranged  to  fall  a  distance  of,  say,  2  feet.  After  each  blow 
the  specimen  is  reversed  and  the  blows  continued  until 
fracture  occurs. 

A  Repeat  Impact  Testing  Machine,  which  is   a  modified 
form  of  that  originally  designed  by  Dr.  Stanton,  is  shown  in 

1  Proc.  Inst.  Mech.  Eng.,  1905,  p.  880. 


144  A  HANDBOOK  OF  TESTING  MATEEIALS 

diagrammatic  outline  in  Fig.  95.  A  is  a  hammer  head  carried 
at  the  end  of  a  lever,  which  is  pivoted  at  B.  The  power  is 
supplied  by  a  belt  00,  which  drives  a  pulley  H,  which  is  in 
turn  attached  to  a  crank  J.  As  this  crank  revolves  it  works  a 
connecting  rod  M,  whose  motion  is  guided  by  a  grooved 
pulley  K.  The  end  of  the  rod  is  thus  caused  to  describe  an 
irregular  elliptical  path,  the  amplitude  of  which  varies  with 
the  position  of  the  pulley  K,  which  is  adjustable.  At  N  is  a 
catch  so  arranged  that  as  the  end  of  the  rod  ascends  it 
engages  with  this  catch  and  raises  the  hammer  to  a  height 
depending  on  the  position  of  L.  The  connecting  rod  then 
moves  forward  and  the  hammer  descends  freely.  The  speci- 
men, shown  in  section  at  D,  is  placed  across  the  knife  edges 
and  gripped  in  a  chuck  attached  to  a  chain  pulley  F.  This 
later  is  connected  to  a  second  chain  pulley  G  on  the  main 
driving  shaft,  the  two  wheels  being  geared  2  to  1.  By  these 
means  the  hammer  is  caused  to  strike  the  specimen  twice  in 
every  revolution,  the  cycle  being  repeated  about  100  times  a 
minute.  L  is  arranged  to  move  along  a  graduated  scale 
showing  directly  the  fall  of  the  hammer.  The  specimen 
under  test  is  usually  about  J  inch  in  diameter,  with  a  groove 
turned  at  its  centre  to  ensure  its  fracture  there.  The  knife 
edges  are  cut  slightly  hollow,  and  a  spring  holds  one  end  of 
the  specimen  in  place.  The  chuck  hold  is  so  arranged  that 
it  does  not  take  any  portion  of  the  hammer  blow,  all  of  which 
comes  on  the  knife  edges. 

Although  not  shown  in  the  diagram,  there  is  an  intervening 
mechanism  between  the  chuck  and  the  pulley  F,  by  which  the 
former  does  not  have  a  uniform  rotation,  but  a  spring  and 
trigger  arrangement  causes  the  specimen  to  have  a  step-by- 
step  motion.  That  is  to  say,  the  specimen  receives  a  blow, 
twists  suddenly  through  180  degrees,  and  remains  stationary 
until  another  blow  is  struck,  when,  after  the  hammer  has 
lifted,  it  again  turns  through  180  degrees.  A  revolution 
counter  records  the  number  of  blows  struck.  When  fracture 
occurs,  the  specimen  falls  away,  the  hammer  head  continuing 
to  fall  first  works  an  electric  switch  which  shuts  down  the 


IMPACT  AND  HAEDNESS  TESTS 


145 


driving  motor  and  then  comes  to  rest  on  a  steel  stop  pin. 
This  machine  is  made  by  the  Cambridge  Scientific  Instru- 
ment Company. 


PLAN 


,  E> 


A 


O 


EDGE 


Ic.  &  Vor 


<2    eclge 
D 


E  LEVATiON    P 

FIG.  96. — Un win's  Apparatus  for  Hardness  Tests. 

Hardness  Tests. — Hardness  tests  may  be  divided  into  two 
chief  classes,  (a)  scratch  tests,  (b)  indentation  tests.  In  the 
first  of  these  methods  a  loaded  diamond  is  pressed  on  the 
polished  surface  of  the  material,  and  the  latter  pulled  so  as  to 

T.M.  L 


146  A  HANDBOOK  OF  TESTING  MATEEIALS 

cause  the  diamond  to  make  a  scratch.  Standardisation  may 
be  taken  either  by  basing  the  hardness  factor  or  "  number," 
as  it  is  generally  termed,  on  the  load  necessary  to  make  a 
scratch  of  standard  width  (the  latter  being  measured  by  a 
microscope),  or  on  the  width  of  scratch  made  by  a  standard 
load.  This  method  is  specially  adapted  for  extremely  hard 
materials,  such  as  rock,  etc.,  and  in  such  cases  indentation 
tests  cannot  be  satisfactorily  applied.  On  the  other  hand, 
it  is  probable  that  for  the  testing  of  ordinary  engineering 
materials  indentation  tests  are  more  reliable  and  easier  to 
standardise. 

In  the  case  of  indentation  tests  a  body  of  some  standard 
form,  such  as  a  knife-edge  of  standard  angle,  or  a  ball 
of  known  diameter,  is  pressed  into  the  material  by  a 
definite  load.  The  hardness  number  is  in  general  based 
on  the  volume  of  the  indentation  produced  by  a  standard 
load. 

One  apparatus  used  in  connection  with  the  indentation  test 
is  shown  in  Fig.  96.  It  consists  of  a  strong  framework  A, 
with  open  sides,  accurately  bored  to  receive  a  ram  C.  The 
knife-edge  D,  which  is  of  square  section,  rests  against  a 
true  face  on  the  bottom  of  the  ram.  To  obtain  a  truly  axial 
load  a  ball  and  socket  joint  is  provided  between  B  and  C. 
The  test  piece,  resting  on  the  bottom  of  the  frame  A,  is 
indented  by  the  knife-edge  D,  care  being  taken  that  the 
indentation  is  not  so  deep  as  to  cause  the  metal  to  spread 
at  the  sides.  The  depth  of  the  groove  thus  formed  is  measured 
by  the  scale  and  vernier  E  as  in  the  punching  test.  A 
series  of  observations  of  indentation  and  load  are  taken, 
from  which  a  constant  is  deduced  which  is  the  measure  of 
hardness. 

The  test  piece  is  usually  about  f  inch  square  and  2j  inches 
long,  and  the  load  is  applied  by  placing  the  apparatus  in  an 
ordinary  testing  machine  and  applying  a  compressive  load. 
It  is  necessary  to  standardise  the  machine  by  measuring  the 
amount  of  compression  which  the  machine  itself  undergoes 
apart  from  the  indentation  of  the  specimen.  Prof.  Unwin  has 


IMPACT   AND   HAKDNESS  TESTS  147 

shown   that  a  relation  between  indentation  and  load   takes 
place  according  to  the  formula— 


where  i  is  the  depth  of  the  indentation  in  inches,  p  the  pressure 
per  inch  of  width  of  knife-edge  producing  the  indentation,  and 
C  a  constant  for  the  material,  termed  the  hardness  number. 
Readings  should  be  taken  at  varying  loads,  and  the  mean 
value  of  C  calculated  from  the  equation  — 

log  C=l*2  log  p—  log  i. 
The  following  are  some  values  obtained  by  Unwin  :— 

Metal.  Value  of  C. 

Cast  steel,  normal.         .....  554'0 

Mild  steel,  normal.         .         .         .         .         .  148*5 

Copper,  annealed  .         .         .         .        ,         .  -  62*0 

,,        unannealed        .         .         .                  .  105*2 

Brass,  No.  1  .         .         .         .                  *         .  221*0 

„      No.  2  .....         .         .  246*0 

Aluminium,  squirted      .         .      ...'".      .         .  41*8 

„           alloy,  cast  .....  103*5 

Lead,  cast      •         .         .                 .         .         .  4*2 

Zinc,  cast       .         .         .         .         .         .         .  40*8 

Messrs.  Calvert  and  Johnson  used,  instead  of  a  knife-edge, 
a  small  truncated  cone,  and  took  as  the  measure  o,f  hardness, 
the  weight  which  would  indent  the  metal  to  a  depth  of  3  J 
milimetres  in  half  an  hour.  In  some  United  States  tests  the 
volume  of  indentation  produced  by  a  pyramidal  point  loaded 
with  a  weight  of  10,000  Ibs.  was  used  to  measure  the  hardness 
of  the  material. 

Brinell's  Ball  Test.  —  Since  in  all  hardness  tests  in  which  the 
indenting  tool  has  a  sharp  point  or  edge  the  latter  is  likely 
to  become  blunt,  it  is  obvious  that  results  may  become  depen- 
dent on  the  condition  of  the  tool,  and  for  this  reason  it  is 
probable  that  a  special  ball  offers  the  best  form  for  making 
the  indentation.  This  is  the  method  employed  by  Brinell. 

L  2 


U8 


A  HANDBOOK  OF  TESTING  MATERIALS 


The  test  consists  in  pressing  a  hardened  steel  ball  into  the 
flat  surface  of  the  specimen  under    a  known  pressure   and 
measuring  the  volume  or  curved  area  of  the  impression. 
Fig.  97  shows  one  form  of  the  apparatus  employed. 


FIG.  97.— Brinell's  Machine. 


Brinell  has  taken  as  a  basis  of  comparison 
Hardness  number  Tofad 


Curved  area  of  impression' 
But  curved  area=2*rf  r— 


Where  I)  is  diameter  of  impression  and  r  radius  of  ball. 
Whence  H.N.=- 


IMPACT  AND   HAKDNESS  TESTS 


149 


The  number  obtained  by  this  formula  will  vary  somewhat 
for  different  value  of  P  and  r,  hence  Brinell  has  fixed  the 
standard  by  taking r= 5  millimetres,  and  P= 3,000 kilogrammes, 
D  being  in  millimetres. 

It  has  been  shown  by  Benedicks  of  Upsala  that  for  balls  of 
different  radius  a  constant  value  is  obtained  by  multiplying 

the  above  hardness  number  by    \/r.     Or  Benedick's  hardness 

number=(Brinell's  H.N.)5\A. 

Various  types  of  machines  for  applying  the  Brinell  test 

have  been  devised,  notably  by  Guillery  and  by  Brinell 
himself. 

The  following  table,  given  by  Prof.  Warren,  of  the 
University  of  Sydney,  gives  a  ready  means  of  determin- 
ing the  hardness  number  from  the  diameter  of  the 
depression  : — 


TABLE  VI. — KELATION  BETWEEN  THE  DIAMETER  OF   THE  IMPRESSION 
AND  BRINELL' s  HARDNESS  NUMBER. 


Hardness  Number  for  the 

Hardness  Number  for  the 

Diameter  of 

Pressure  in  kgs. 

Diameter  of 

Pressure  in  kgs. 

Impression. 

Impression. 

Mm. 

1 

Mm. 

3,000 

500 

3,000 

500 

2-00 

946 

158 

2'75 

495 

83 

2-05 

898 

150 

2-80 

477 

80 

2-10 

857 

143 

2-85 

460 

77 

2-15 

817 

136 

2-90 

444 

74 

2-20 

782 

130 

2-95 

430 

73 

2-25 

744 

124 

2-30 

713 

119 

3-00 

418 

70 

2-35 

683 

114 

3-05 

402 

67 

2-40 

652 

109 

3-10 

387 

65 

2-45 

627 

105 

3-15 

375 

63 

2-50 

600 

100 

3-20 

364 

61 

2-55 

578 

96 

3-25 

351 

59 

2-60 

555 

93 

3-30 

340 

57 

2-65 

532 

89 

3-35 

332 

55 

2-70 

512 

86 

3-40 

321 

54 

150 


A  HANDBOOK  OF  TESTING  MATERIALS 


TABLE  VI. — Continued. 


Diameter  of 
Impression. 
Mm. 

Hardness  Number  for  the  . 
Pressure  in  kgs. 

Diameter  of 
Impression. 
Mm. 

Hardness  Number  for  the 
Pressure  in  kgs. 

3,000 

500 

3,000 

500 

3-45 

311 

52 

5-20 

131 

2118 

3  -50 

302 

50 

5-25 

128 

21-5 

3  '55 

293 

49 

5-30 

126 

21*0 

3-60 

286 

48 

5-35 

124 

20-6 

3-65 

277 

46 

5-40 

121 

20-1 

3-70 

269 

45 

5  '45 

118 

19-7 

3-75 

262 

44 

5-50 

116 

19-3 

3-80 

255 

43 

5.55 

114 

19-0 

3-85 

248 

41 

5-60 

112 

18-6 

3-90 

241 

40 

5-65 

109 

18-2 

3-95 

235 

39 

5-70 

107 

17'8 

5*75 

105 

17'5 

4-00 

228 

38 

5-80 

103 

17-2 

4-05 

223 

37 

5*85 

101 

16-9 

4-10 

217 

36 

5-90 

99 

16-6 

4-15 

212 

35 

5-95 

97 

16-2 

4-20 

207 

34-5 

4-25 

202 

33-6 

6-00 

95 

15-9 

4-30 

196 

32-6 

6-05 

94 

15-6 

4-35 

192 

32-0 

6-10 

92 

15-3 

4-40 

187 

31-2 

6-15 

90 

15-1 

4-45 

183 

30-4 

6-20 

89 

14-8 

4-50 

172 

29-7 

6-25 

87 

14-5 

4'55 

174 

29-1 

6-30 

86 

14-3 

4-60 

170 

28-4 

6-35 

84 

14-0 

4-65 

166 

27'8 

6-40 

82 

13-8 

4-70 

163 

27-2 

6-45 

81 

13-5 

4-75 

159 

26-5 

6-50 

80 

13-3 

4-80 

156 

25-9 

6-55 

79 

13-1 

4-85 

153 

25-4 

6-60 

77 

12-8 

4-90 

149 

24-9 

6-65 

76 

12-6 

4-95 

146 

24-4 

6-70 

74 

12-4 

6-75 

73 

12-2 

5-00 

143 

23-8 

6-80 

71-5 

11-9 

5-05 

140 

23-3 

6-85 

70 

11-7 

5-10 

137 

22-8 

6-90 

69 

11-5 

5-15 

134 

22-3 

6-95 

68 

11-3 

Professor  Warren  gives  some  interesting  figures  showing 
the  relation  between  the  tensile  strength  and  the  hardness  as 
obtained  by  Brinell's  ball  test. 


IMPACT  AND  HAEDNESS  TESTS 
TABLE  VII. 


151 


Tensile  Strength. 
Tons  per  sq.  in. 

Brinell's  Hardness 
Number. 

Ratio  of  the  Tensile 
Strength  to  Hardness 
Number. 

28-9 

170 

•170 

30-2 

149 

•203 

25-3 

141 

•180 

2,3-6 

140 

•183 

27-0 

140 

•193 

25-8 

140 

•184 

24-9 

137 

•182 

25-6 

134 

•191 

Mean     26'7 

143-9 

•186 

The  above  figures  were  obtained  on  structural  steel,  the  ball 
being  10  millimetres  diameter  ;  pressure  3,000  kilogrammes. 

It  will  be  observed  that  the  value  obtained  by  dividing  the 
actual  tensile  strength  by  the  Brinell's  hardness  number  is 
fairly  constant  for  the  same  quality  of  steel. 

In  the  case  of  axle  steel  the  following  was  obtained — 

TABLE  VIII. 


Tensile  Strength. 
Tons  per  sq.  in. 

Brinell's  Hardness 
Number. 

Ratio  of  the  Tensile 
Strength  to  Hardness 
Number. 

34-0 
36-5 
33-9,5 

167 
168 
205 

•202 
•216 
•165 

Mean     34-8 

180 

•194 

Dillner,  of  Stockholm,  has  investigated  this  same  relation 
between  tensile  strength  and  hardness  number,  and  found 
with  only  a  mean  error  of  3'3  per  cent,  that  the  tensile 
strength  in  tons  per  sq.  in.  for  steels  having  a  hardness 
number  below  175  could  be  obtained  by  multiplying  the 


152  A  HANDBOOK  OF  TESTING  MATERIALS 

hardness  number  by  0*230  when  the  indentation  was  made 
transversely  to  the  direction  of  rolling,  or  0*225  when  made 
in  the  direction  of  rolling. 

The  "  Scratch  "  Test  is  used  by  Prof.  Turner  in  his  "  scleor- 
meter."  This  consists  of  a  perfectly  balanced  lever,  which 
has  a  diamond  point  at  one  end.  The  whole  arrangement 
can  be  moved  from  side  to  side,  so  as  to  make  a  scratch  on 
the  smooth  surface  of  the  metal  to  be  tested.  The  load  on 
the  point  can  be  varied  by  adding  weights  to  a  small  scale  pan 
on  the  lever,  and  the  weight  in  grams  acting  on  the  diamond 
point  required  to  produce  a  standard  scratch  is  used  as  a 
measure  of  the  hardness  of  the  metal. 

In  connection  with  hardness  tests  an  important  communi- 
cation upon  the  subject  was  compiled  by  Prof.  Thomas 
Turner,1  M.Sc.,  from  which  the  following  observations  are 
obtained.  He  compared  four  methods,  viz.:  (1)  Turner's 
sclerometer;  (2)  Shore's  scleroscope ;  (3)  Brinell's  test; 
(4)  Keep's  test.  It  may  be  mentioned  that  method  (2) 
involves  the  use  of  a  new  patent,  viz.,  the  scleroscope.  In 
this  instrument  there  is  a  small  cylinder  of  steel  with  a 
hardened  point.  This  is  allowed  to  fall  on  the  smooth  surface 
of  the  metal  to  be  tested,  and  the  hardness  of  the  material 
is  taken  by  measuring  the  rebound.  Prof.  Turner  says : 
"  Each  form  of  test  has  its  advantages  and  its  limitations- 
The  sclerometer  is  cheap,  portable,  and  easily  applied,  but  it  is 
not  applicable  to  materials  which  do  not  possess  a  fairly  smooth 
reflecting  surface,  and  the  standard  scratch  is  only  definitely 
recognised  after  some  experience.  The  Shore  test  is  simple, 
rapid,  and  definite  for  materials  for  which  it  is  suited,  and 
appears  likely  to  have  an  important  future.  But  further 
information  is  yet  needed  as  to  the  exact  property  which  is 
measured  by  this  form  of  test.  As  shown  by  De  Ereminville, 
the  result  obtained  varies  somewhat  with  the  size  and  thick- 
ness of  the  sample,  while  if  the  test  piece  is  supported  on  a 
soft  material  such  as  a  plasticine  the  results  are  valueless. 
It  may,  however,  be  pointed  out  that  indiarubber  gives  a 

1  Journal  of  the  Iron  and  Steel  Institute,  1909. 


IMPACT   AND   HAEDNESS   TESTS  153 

rebound  of  23,  which  is  equal  to  that  of  mild  steel ;  while  I 
have  found  light  soft  pine-wood  give  a  rebound  of  40,  which 
is  nearly  double  as  great  as  that  of  grey  cast-iron.  Curiously 
enough  hard  wood,  like  teak,  gives  a  rebound  of  about  12, 
while  some  samples  are  considerably  lower  than  this.  As 
illustrating  the  influence  of  the  support,  a  sample  of  excep- 
tionally hard  rolled  copper  about  -^  of  an  inch  in  thickness, 
when  supported  on  a  block  of  hard  steel  and  tested  with  the 
blunt  or  "  magnified  "  hammer  supplied,  gave  a  value  of  30, 
which  was  increased  to  34  when  the  copper  was  supported  on 
wood.  A  sample  of  brass  only  gave  a  value  of  17,  and  yet 
this  brass  would  scratch  the  copper,  while  the  copper  would 
not  scratch  the  brass.  From  these  results  it  is  evident  that 
the  Shore  test  is  only  applicable  to  a  certain  class  of  -sub- 
stances. It  appears  to  test  what  may  be  termed  the  "  elastic 
hardness,"  and  gives  high  results  with  metals  in  the  "  worked 
hard  "  or  ecroui  condition  ;  values  which  are  not  fully  con- 
firmed by  the  tool  or  by  the  sclerometer.  My  tests  appear  to 
show  that  good  results  are,  however,  obtained  with  glass  and 
with  porcelain,  as  well,  of  course,  as  with  most  metals.  The 
Brinell  test  is  specially  useful  for  constructive  material;  it 
is  easily  applied  and  definite,  and  is  now  of  all  hardness  tests 
the  one  most  employed.  It  appears  to  give  satisfactory  results 
with  wood,  but  cannot  be  applied  to  very  brittle  materials 
such  as  glass,  or  to  hard  minerals.  Keep's  test  is  specially 
suited  for  castings  of  all  kinds,  as  it  records  not  merely  the 
surface  hardness,  but  also  that  of  the  whole  thickness,  and 
gives  indications  of  blowholes,  hard  streaks,  and  spongy 
places.  Obviously  it  can  only  be  applied  to  materials  the 
hardness  of  which  is  less  than  that  of  hardened  steel." 

Curiously  enough,  however,  it  may  be  noted  that  all  four 
methods  give  comparative  results  for  all  pure  metals  in  their 
normal  condition.  The  following  results,  obtained  from  the 
experiments  of  Prof.  Turner,  will  give  an  idea  of  the 
closeness  of  agreement  and  the  actual  values  of  various 
materials. 

Other    tests    of    hardness    are    grinding,    machining    and 


154 


A  HANDBOOK  OF  TESTING  MATERIALS 


drilling  tests,  but  the  methods  most  used  are  those  described 
above. 

TABLE  IX. — HARDNESS  SCALES  COMPARED. 


Metal. 

Turner. 
(Sclerometer.) 

Scleroscope. 

Brinell. 

Keep. 

6. 

Lead     .         . 

1-0 

1-0 

1-0 

Tin       .    .  .  .         . 

2-5 

3-0 

2-5 

Zinc 

6-0 

7-0 

7-5 

Copper,  soft  . 
,,       hard 

8-0 

8-0 
12-0 

12-0 

Angle 

Softest  iron  . 

15-0 

.  

14-5 

varies 

Mild  steel     . 

21-0 

22-0 

16-24 

from  0° 

Soft  cast-iron 
Eail  steel      .         . 

21-24 
24-0 

24-0 
27-0 

24-0 
26-35 

to  90°. 

Hard  cast-iron 

36-0 

40-0 

35-0 

Hard  white  iron    . 

72-0 

70-0 

75-0 

Hardened  steel     . 

— 

95-0 

93-0 

Combined  Static  and  Shock  Tests. — At  a  recent  meeting 
of  the  Physical  Society  (October,  1910)  Mr.  Kogers  presented 
a  paper  describing  the  results  of  tests  made  upon  steel 
specimens  subjected  to  stresses  caused  (simultaneously)  by 
bending  and  shock,  or  impact.  It  appears  that  the  results 
would  be  easier  to  interpret  if  the  static  load  were  either 
tension  or  compression.  The  work  of  Mr.  Eogers  is  important, 
as  the  author  believes  it  to  be  the  first  published  on  combined 
static  and  impact  tests.  It  should  suggest  the  lines  of  further 
interesting  experiments. 


CHAPTEK   VIII 

SHEAR    AND    MISCELLANEOUS    TESTS 

DIRECT  shear  or  "  rivet "  tests,  that  is  to  say  shear  tests  as 
distinct  from  torsion  tests,  are  not  very  frequently  carried  out, 
owing  to  the  difficulty  of  ensuring  pure  shear  without  hending. 
When  such  experiments  are  made  they  are  generally  performed 
in  an  ordinary  "  omnibus  "  machine  arranged  for  tension  or 
compression,  use  being  made  of  a  special  form  of  shackle. 
There  are  many  forms  of  the  latter,  and  such  will  readily 
suggest  themselves  to  the  student  as  modifications  of  the 
single  example  taken. 

Shearing  Shackles. — This  apparatus,  shown  in  Fig.  98,  con- 
sists of  two  rectangular  blocks  A  and  B,  which  are  bolted 
together  by  the  four  bolts  C,  D,  E,  F.  Down  the  centre  of 
these  blocks  is  cut  a  rectangular  channel  G,  in  which  a 
rectangular  piece  H  is  allowed  to  slide.  The  three  discs 
K,  L,  and  M  fit  accurately  in  a  hole  which  is  bored  through 
A  and  B,  and  are  fixed  in  position  by  the  hollow  nuts  N  and  0. 
The  specimen  is  supplied  in  the  form  of  a  cylindrical  bar, 
which  accurately  fits  inside  the  holes  in  K,  L  and  M.  When 
the  bar  is  in  position  the  load  is  applied  to  H,  and  the  specimen 
is  sheared  off  at  the  joints  between  K  and  L  and  L  and  M,  the 
strength  in  double  shear  thus  being  ascertained.  It  is  important 
that  the  faces  of  K,  L  and  M  should  be  perfectly  true,  as  if 
there  is  any  space  between  them  the  material  is  not  in  pure 
shear,  but  partly  in  bending. 

Shear  Tests. — With  this  apparatus  tests  on  materials  can 
be  carried  out  in  either  single  or  double  shear.  The  bearing 
surface  should  always  be  kept  as  large  as  possible,  so  that 
when  making  tests  in  single  shear,  the  specimen  should  be 


156 


A  HANDBOOK  OF  TESTING  MATEEIALS 


pushed  so  far  through  the  middle  die  that  it  just  misses  fouling 
the  end  die. 


Z 

0 

i 

id 

J 

uJ 


To  avoid  errors  due  to  bending  the  specimen  should  be  a 
very  good  fit  in  the  dies,  and  for  the  same  reason  there  should 
be  no  clearance  between  the  latter  when  in  position. 


SHEAE  AND   MISCELLANEOUS  TESTS 


157 


The  following  results  were  obtained  for  mild  steel,  wrought- 
iron,  and  cast-iron  in  both  double  and  single  shear  :— 

TABLE  X. 


Material. 

Method  of 
Shear. 

Diameter. 
Inches. 

Area. 
Sq.  in. 

Load. 
Tons. 

Shear  Stress, 
Tons,  per 
sq.  in. 

Mild  steel 

Double 

•875 

•601 

21-66 

18-02 

» 

Single 

•875 

•601 

10-90 

18-14 

Wrought  -iron 

Double 

•877 

•606 

20-97 

17-32 

»           » 

Single 

•877 

•606 

10-38 

17-20 

Cast-iron 

Double 

•871 

•596 

15-12 

12-70 

»       » 

Single 

•874 

•600 

7-48 

12-47 

As  will  be  seen  from  the  table,  the  strength  of  a  material  in 
double  shear  is  about  twice  that  in  single  shear. 

In  addition  to  thus  testing  in  single  and  double  shear  some 
interesting  and  useful  results  can  be  obtained  by  testing  in 
shear  specimens  cut  from  the  same  bar  as  those  specimens 
tested  in  tension.  From  such  results  valuable  information 
can  be  gained  as  to  what  proportion  of  the  tensile  stress  is  to 
be  taken  for  a  corresponding  safety  factor  in  shear. 

The  following  table  gives  actual  results  : — 

TABLE  XI. 


Material. 

Breaking 
Tension. 

Shear  Stress. 

Ratio. 

Tons  per 

sq.  in. 

Best  Staffordshire  iron     . 

24-41 

19-35 

•793 

Yorkshire  iron 

23-13 

18-02 

•781 

Mild  steel  bar           ... 

28-64 

20-04 

•700 

Steel  boiler  plate     . 

27-17 

18-68 

•688 

Spring  steel     .... 

48-10 

30-84 

•642 

Copper  plate 

14-33 

9-96 

•695 

It  is  probable  that,  with  such  tests,  a  pure  shear  is  never 
obtained  because  of  the  complication  due  to  bending.  The 
most  satisfactory  method  of  obtaining  pure  shear  is  that  of 


158 


A  HANDBOOK  OF   TESTING  MATERIALS 


SHEAR  AND  MISCELLANEOUS  TESTS 


159 


using  a  hollow  specimen  for  a  torsion  test.  At  the  same  time  the 
results  obtained  of  this  "  rivet  shear  "  test  are  valuable,  as  they 
are  obtained  under  conditions  such  as  take  place  in  practice. 

Punching  Tester  (Fig.  99).  —  The  apparatus  consists 
essentially  of  a  steel  cylinder  A  which  slides  up  and  down 
in  a  cylindrical  guide  B.  The  test  piece,  consisting  of  a  plate 
of  the  required  material,  is  secured  tightly  between  the  bottom 


5000 


10 
Q 
* 

:>  3000 

0 

a 


t    2ooo 
0 

«c 

0 

__j     JOOO 


PUNCHING  TESTS. 
MILO  STEEL 


OBSERVED. 


-2 

//V 
FIG.  100.— Punching  Test  on  Mild  Steel. 

of  B  and  the  base  plate  C  by  means  of  the  bolts  D,  E.  The 
punch  is  fastened  to  the  cylinder  A,  while  the  die  fits  in  a 
corresponding  recess  in  the  base  plate  C.  The  load  is  applied 
vertically  downwards  on  the  cylinder  A,  and  the  punch  thus 
driven  through  the  test  plate.  The  strain  of  the  metal  can  be 
read  for  any  given  load  by  means  of  a  scale  fitted  to  A,  and 
a  vernier  attached  to  the  guide  B.  The  tests  can  also  be 
automatically  recorded  by  the  following  arrangement.  The 
downward  movement  of  A,  and  consequently  the  yielding  of 
the  specimen,  is  transmitted  by  means  of  a  rack  and  pinion, 
through  a  stretched  cord  to  a  drum  G,  which  thus  rotates  in 


160  A  HANDBOOK  OF  TESTING  MATERIALS 

proportion  to  the  strain  of  the  test  plate.  The  pencil  is  moved 
along  the  axis  of  the  drum  by  means  of  a  cord  or  wire  from 
the  loading  mechanism,  its  movement  being  proportional  to 
the  load  on  A.  Hence  the  diagram  recorded  is  a  stress-strain 
curve,  and  the  work  done  in  punching  out  the  plate  can  be 
obtained  from  it  in  the  usual  way. 

Punching  Tests.— By  means  of  this  apparatus,  load-strain 
diagrams  can  be  obtained  either  autographically  or  by  plotting 
simultaneous  readings  of  load  and  strain,  the  latter  being 
obtained  by  means  of  the  vernier.  Load  calibration  of  the 
autographic  diagram  is  performed  by  observing  the  maximum 
load  which  is  reached  during  the  test.  This  load  will 
correspond  with  the  highest  point  on  the  curve,  and  thus 
the  load  scale  can  be  determined.  The  strain  is,  of  course, 
obtained  knowing  the  thickness  of  the  plate  being  punched. 
Fig.  100  shows  diagrams  obtained  by  each  of  these  two 
methods  on  the  same  plate  of  mild  steel  with  the  same  punch. 
These  diagrams  afford  a  simple  method  of  finding  the  work 
done  in  punching  the  hole,  equalling,  as  it  does,  merely  the 
area  under  the  curve  to  the  correct  scale. 

Eesistance  to  punching  is  practically  a  shearing  resistance. 
Then  if  d= diameter  of  hole,  and  £=thickness  of  plate  — 

Shearing  resistance  of  plate  per  sq.  in. 

maximum  load 

irdt  ' 

For  comparison  these  quantities  have  been  calculated  for 
the  two  curves,  Fig.  100. 

Mild  Steel  Specimen. 

j  Diameter  of  punch =*870  inches. 

( Thickness  of  plate='359      ,, 
From  autographic  diagram. 
Maximum  load  =  43, 800  Ibs.  per  sq.  in. 
Work  done  in  punching  hole =700  ft.  Ibs. 

,r    .  P          43,800 

Maximum  punching  resistance  of  plate  =  —=-=  — 


=44,750  Ibs.  per  sq.  in. 


SHEAR  AND  MISCELLANEOUS   TESTS 

Diagram  from  observed  readings. 
Work  done  in  punching=725  ft.  Ibs. 

AT     •  45,200 

Maximum  punching  resistance— :~ 


161 


"7rX'87X-359 
=46,100  Ibs.  per  sq.  in. 

Tests  of  Steel  Balls. — The  testing  of  steel  balls  in  a 
satisfactory  manner  presents  some  difficulty,  as  it  is  not  an 
easy  matter  to  obtain  a  surface  which  will  not  become  indented 


Hardened  Steel 


^Hardened  Steel 
Sectional  Elevabion  .  Side  View. 

FIG.  101. — Apparatus  used  for  Testing  Steel  Balls. 

before  the  pressure  becomes  sufficiently  great  to  crush  the 
ball. 

Up  to  sizes  of  about  f  inch  diameter  hardened  steel  plates, 
between  which  to  crush  the  ball,  can  be  used  with  moderate 
success,  but  with  balls  of  larger  diameter  than  this,  the  plates 
either  indent,  or  if  sufficiently  hard,  actually  crack. 

A  method  of  testing  the  larger  sizes  of  balls  at  the  East 
London  College,  which  has  been  found  to  answer  very 
successfully,  is  roughly  as  follows.  The  ball  to  be  tested  is 
supported  between  two  other  balls,  these  in  turn  exactly  fitting 

T.M.  M 


162 


A  HANDBOOK  OF  TESTING  MATEKLALS 


into  turned  recesses  in  hardened  steel  blocks.  With  such  an 
arrangement  the  centre  ball,  i.e.,  the  one  to  be  tested,  breaks 
first,  almost  without  exception,  and  in  addition  a  point  contact 
is  obtained.  Fig.  101  shows  the  apparatus  employed. 


CRUSHING  LOAD  IN  TONTS. 

0  ;o  2o  .30  <*o  So  <oo  ro  8, 

/ 

/ 

/ 

^ 

s 

/ 

/ 

/ 

/ 

/ 

s 

/ 

/ 

^ 

^ 

^ 

or  BALL  IN  INCHES. 
PIG.  102.— Steel  Ball  Tests.     Published  by  "  Machine  Co." 

The  following  table,  published  by  the  Machine  Company, 
Coventry,  gives  the  crushing  strength  of  steel  balls  up  to 
1J  inch  in  diameter  :— 

TABLE  XII. 


Size  of  Ball. 

Crushing  Load. 

Size  of  Ball. 

Crushing  Load. 

Size  of  Ball. 

Crushing  Load. 

Inch. 

Tons. 

Inch. 

Tons. 

Inch. 

Tons. 

L 

8 

A 

•574 
•893 

t 

8-70 
11-82 

1J 
1& 

43-75 
49-05 

^i 

1-297 

A 

15-61 

U 

58-00 

•3\ 

2-009 

21-65 

l| 

64-70 

i 

2-99 

1 

29-90 

ii 

73-60 

A 

4-01 

| 

34-80 

f 

6-39 

i 

41-25 

These  results  are  shown  graphically  in  Fig.  102. 


SHEAE  AND  MISCELLANEOUS  TESTS 


163 


If  a  curve  be  plotted  between  the  squares  of  the  diameters 
of  the  balls  and  the  crushing  load,  an  approximately  straight 
line  is  obtained,  showing  that  a  proportionality  exists  between 
these  two  quantities. 

The  most  usual  form  of  failure  is  a  vertical  fracture  extend- 
ing the  whole  length  of  the  ball. 

Sometimes,  however,  the  ball  breaks  into  several  pieces,  or 
it  may  be  partly  crushed  to  powder. 

Roller  Test. — When  a  cast-iron  specimen  is  tested  as  a 
roller,  fracture  occurs  in  a  longitudinal  vertical  plane  through 
the  axis  of  the  specimen,  loose  wedge-shaped  pieces  falling 
out  along  the  two  lines  of  contact.  The  stress,  of  course,  is 
variable  over  the  section,  but  in  the  test  given  below  the 
compressive  stress  has  been  calculated  as  distributed  uniformly 
over  the  projected  area  of  the  roller. 

TABLE  XIII. 
COMPRESSION  TEST— CAST-IRON. 


No.  of 
Specimen. 

Diameter. 

Area. 

Length. 

Crushing 
Load. 

Crushing 
Stress. 

Tons. 

Per  sq.  in. 

1 

•730" 

•418 

2-40 

24-43 

58-4 

T 

e  steel        a. 

j         Boiler. 

•726" 

1-833 

2-525 

24-66 

15-59 

Rough  Shop  Tests. — In  most  specifications  for  materials  it 
is  usual  to  specify  certain  comparatively  rough  tests  besides  the 
more  refined  methods  of  machine  testing  such  as  have  been 
previously  described.  Thus  in  the  case  of  cast-iron  it  is  usual 
to  insert  a  clause  to  the  effect  that,  at  every  pouring,  one  or  two 
bars  shall  be  cast  having  dimensions  in  the  neighbourhood  of 
8  to  4  feet  long,  and  having  a  section  from  2  inches  by  1  inch 
to  1  inch  square ;  and  that  when  such  bars  are  placed  on 
supports,  say  3  feet  apart,  they  shall  support  a  central  load  of 
a  specified  amount.  The  Admiralty  specification  for  cast-iron 
is  a  breaking  load  of  2,000  Ibs.  on  a  beam  1  inch  square  with 

M  2 


164 


A  HANDBOOK  OF  TESTING-  MATERIALS 


supports  1  foot  apart.  Such  tests  are  frequently  performed  in 
a  foundry  merely  by  placing  the  bar  on  the  edges  of  two 
moulding  boxes  placed  the  specified  distance  apart,  and 
hanging  foundry  weights  to  the  centre  until  fracture  occurs. 
The  weights  are  then  placed  on  a  weighing  machine,  and  it  is 
at  once  seen  whether  the  bar  comes  within  the  specification. 
When,  however,  as  is  sometimes  done,  deflections  are  specified, 
and  in  foundries  where  a  large  amount  of  Government  and 
similar  work  is  carried  out,  proper  machines  are  used.  Fig.  103 
indicates  in  outline  the  general  principle  of  one  very  good  type 
of  machine  for  this  purpose.  It  will  be  seen  that  the  load  is 


W/////////////////^^^^ 

FIG.  103. — Small  Beam  Testing  Machine  for  Cast  Iron. 

applied  by  a  hand-wheel  and  screw,  and  this  load  is  balanced 
and  measured  by  moving  a  weight  along  a  graduated  beam. 
In  the  case  of  the  more  powerful  machines  the  load  is  applied 
through  compound  gearing.  The  moving  weight  is  made  so 
that  it  can  be  varied  by  placing  disc  weights  on  to  it,  and  thus 
making  the  machine  capable  of  accurate  measurement  over 
a  wide  range  of  beam  sizes. 

Eough  mechanical  tests  for  ductile  materials  are  those 
known  as  cross-bending,  folding  or  doubling  tests.  Thus  the 
Admiralty  specify  that  specimens  of  steel  forgings  1  inch 
square  shall  be  capable  of  being  bent  cold  through  an  angle  of 
180°  over  a  radius  not  greater  than  \  inch.  Specimens  of 
copper  pipes  must  stand  bending  through  180°  cold  until  the 


SHEAK  AND  MISCELLANEOUS  TESTS  165 

two  sides  meet,  and  of  hammering  to  a  fine  edge  without 
cracking.  The  method  of  carrying  out  such  tests  is  obvious, 
but  it  must  be  borne  in  mind  that  to  a  certain  degree  such 
tests  depend  to  a  more  or  less  extent  upon  the  skill  of  the 
smith  who  performs  them,  and  it  is  necessary  that  they  should 
always  be  performed  by  a  skilful  and  unbiassed  hand,  as 
otherwise,  except  in  the  case  of  materials  which  easily  fulfil 
the  test,  it  is  comparatively  easy  to  cause  the  material  to 
fail. 

;  Tests  on  Wires. — Many  instructive  experiments,  especially 
by  way  of  preliminary  to  large  size  specimens,  can  be  carried  out 
on  wires.  A  wire  of  iron  or  steel  is  stretched  about  O'OOl  inch 
per  ton  per  sq.  inch  stress,  and  as  elastic  extension  can  be  taken 
up  to,  say  10  tons  per  sq.  inch,  this  is  equivalent  to  a  maximum 
extension  of  O'Ol  inch  per  foot.  If  a  wire  from  20  to  100  feet 
long  is  employed,  deflections  are  obtained  of  from  0'2  inch 
to  1  inch,  and  such  can  be  easily  and  with  fair  accuracy  read 
by  means  of  an  ordinary  scale  and  vernier.  In  all  tension 
tests  on  long  wires  it  is  desirable,  in  order  to  eliminate 
temperature  effects  and  the  deflection  of  the  supports,  to 
suspend  two  wires  of  the  same  material  side  by  side,  one  of 
which  is  held  taut  by  a  fixed  load  and  carries  the  scale,  while 
the  loaded  wire  carries  the  vernier.  When  very  long  wires 
are  employed  it  is  necessary  to  carry  the  wires  over  pulleys, 
and  in  order  to  eliminate  the  friction  of  the  latter  it  is 
necessary  to  take  two  sets  of  readings  with  increasing  and 
decreasing  load.  The  mean  of  these  two  gives  the  true 
deflection  without  friction.  When  short  wires  are  tested  in 
tension  it  is  necessary  to  employ  some  magnifying  arrange- 
ment for  the  extension.  This  can  be  performed  by  arranging 
a  small  mirror  so  arranged  as  to  be  tilted  by  the  extension 
of  the  wire.  The  deflection  of  the  mirror  is  seen  either  by 
arranging  a  source  of  light  so  that  the  motion  of  the  mirror 
moves  a  beam  of  light  across  a  scale,  as  seen  in  the  sphingo- 
meter  (see  page  68),  or  else  a  telescope  is  moved,  as  in  the 
Bauschinger  extensometer  (see  page  61).  Remembering  that 
the  angle  turned  through  by  the  beam  of  light  is  twice  the 


A  HANDBOOK  OF  TESTING  MATERIALS 


angle  moved  by  the  mirror,  it  is  generally  a  simple  matter  to 
calculate  the  extension  of  the  wire  from  the  direct  readings. 

Prof.  Burr  has  devised  an  ingenious  method  of  taking- 
autographic  diagrams  with  wires.  A  long  wire  is  suspended, 
and  carries  at  its  lower  end  a  fair  sized  bucket.  A  pencil  gear 
is  attached  to  the  wire  so  that  as  it  extends  it  draws  a  line  down 
a  sheet  of  paper  attached  to  a  drum.  Close  to  the  bucket  at 
the  end  of  the  wire  is  a  second  bucket  filled  with  sand  and 
provided  with  an  outlet  so  that  this  sand  can  run  out  into  the 
first  bucket.  The  bucket  of  sand  is  suspended  by  a  spring 
,  and  a  cord  in  such  a 

manner  that,  as  the  sand 
runs  out,  the  bucket  be- 
comes lighter,  allowing  the 
spring  to  contract,  and 
turning  the  drum  round 
on  its  axis  by  means  of  a 
second  cord,  also  attached 
to  the  spring.  It  is 


Extension 


FIG.    104.— Work  done  in    Breaking 
Specimen. 


obvious,  therefore,  that  the 
angular  motion  of  the 
recording  drum  will  be 
proportional  to  the  load,  while  the  movement  of  the  pencil 
gear  will  be  proportional  to  the  extension.  The  result  is  a 
stress-strain  curve  drawn  on  the  sheet  attached  to  the 
drum. 

Work  done  in  Fracturing  a  Specimen. — It  is  clear  from  the 
fact  that  since  work  done  is  equal  to  force  into  distance,  and 
that  the  ordinary  so-called  stress-strain  curve  shows  the 
relation  between  load  and  distance  moved  by  the  same, 
then 

Work    done     in     fracturing      specimen  =/lde,   which   is 

clearly  the  area  shown  in  Fig.  104  by  the  cross-hatched 
lines.  This  should  be  measured  by  the  student,  and  the 
work  done  in  fracturing  the  bar  calculated  per  pound 
and  cubic  inch  of  material.  Prof.  Marten  has  recently  stated 


SHEAR  AND  MISCELLANEOUS  TESTS 


167 


.After  cold  hammering 
— ---  -  -B  s,  workin 


N 


a  rather  important  point  in  connection  with  the  area  thus 
obtained.1 

If  we  draw  round  the  curve  of  load  and  extension  a  circum- 
scribing rectangle,  then  he  calls  the  ratio  of  the  area  of  the 
load-extension  diagram 
to  the  area  of  the  cir- 
cumscribing rectangle  £ . 
The  important  and 
somewhat  curious  point 
is  that  £  is  practically 
a  constant  for  all  con- 
ditions of  the  same 
material,  whether  such 
conditions  are  produced 
by  hammering,  anneal- 
ing, or  any  other  treat- 
ment. Thus  in  Fig.  105 
two  curves  are  shown. 


Annealed 


Q 


Extension 


FIG.  105. — Load-Extension  Curves  showing 
Effect  of  Annealing  on  Mild  Steel. 


One  for  wrought-iron  after  long- 
continued  cold  hammering  and  working,  and  another  for  the 
same  material  after  annealing.  Then 

AreaDHKLC    Area  DMNQO     > 


Area  ABCD 


AreaDEEG 


This  probably  only  applies  to  mild  steel  and  wrought-iron, 
but  it  would  be  worth  the  student's  while  to  see  if  he  can  get 
any  relation  which  remains  fairly  constant  for  different 
changes  of  state. 

1  Zustandsdnderungen  der  Metalle  infolge  von  Festigkeitslea?ispruchimgen. 
A.  Marten,  Preuss.  Akad.  Wiss.  Berlin,  Site.  Ber.  11,  pp.  209—220,  19io. 


CHAPTER   IX 

ALTERNATING    STRESS    TESTS 

Alternating  Stress  Machines. — Many  structures  or  parts  of 
machines  are  subject  to  alternating  stresses,  that  is  to  say 
the  load  on  them  is  constantly  being  increased  or  decreased, 
and  in  many  cases  reversed.  The  diagonal  bracing  in  the 
centre  of  a  bridge,  a  steam-engine  connecting  rod,  or  a  railway- 
carriage  axle  are  typical  examples.  It  is  important,  therefore, 
that  materials  subject  to  such  stresses  should  be  tested  under 
similar  conditions,  and  the  following  machines  have  been 
devised  to  that  end  : — 

The  pioneer  of  this  type  of  test  was  Wohler,  who,  in  1871, 
published  valuable  researches  with  reference  to  the  effect  of 
alternating  stress  upon  the  strength  of  materials.  Other 
prominent  workers  in  the  same  field  have  been  Prof.  J.  0. 
Arnold,  Captain  Sankey,  and  Dr.  Stanton,  all  of  whom  have 
invented  machines  capable  of  performing  alternating  stress 
tests.  Such  tests  are  useful  for  experimental  investigations, 
and  are  of  advantage  in  some  commercial  cases.  The  static 
test  will  probably  always  remain  the  chief  method  used  in 
commercial  work.  It  is,  however,  desirable  that  the  value  of 
alternating  stress  experiments,  especially  when  applied  to  new 
steel  and  other  alloys,  should  not  be  underrated. 

Wohler's  Machine  for  Testing  Alternating  Torsional 
Stresses. —  This  is  illustrated  in  Fig.  106.  The  test  bar  A  is  a 
simple  cylindrical  bar  with  enlarged  ends,  held  in  suitable 
chucks  and  supported  by  two  bearings  B,  C. 

To  the  end  of  the  mandril  passing  through  the  bearing  C 
is  attached  a  lever  D,  which  carries  knife-edges  at  its  end.  H  is 
a  vertical  rod  attached  at  its  lower  end  to  a  horizontal  lever  P, 
and  having  at  E  and  F  adjustable  collars  which  bear  on  the 


170  A  HANDBOOK  OF  TESTING  MATEEIALS 

knife-edges.  The  lever  P,  which  is  pivoted  at  G,  is  moved 
up  and  down  by  the  connecting  rod  Q,  and  arrangements  are 
made  by  which  this  latter  lever  can  be  put  rapidly  in  and  out 
of  gear ;  also  by  means  of  a  slotted  link  in  P  the  stroke  of  the 
latter  can  be  varied.  It  will  thus  be  seen  that  the  vertical 
oscillations  of  Q  are  transformed  to  twisting  oscillations  of  the 
specimen  A.  The  reaction  of  the  torque  thus  transmitted  is 
taken  by  means  of  the  system  of  levers  J  Ji,  K  Kb  etc.,  to  the 
springs  L  LI.  By  adjusting  the  nuts  at  E  and  F  the  stroke  of 
D  can  be  varied  so  as  to  give  equal  stresses  in  opposite 
directions.  N  Niand  M  MI  are  then  adjusted,  so  that  the  contacts 
at  B  and  RI  are  alternately  lifted  against  the  spring  by  the 
reaction  of  the  torque  given  to  the  specimen.  Different  stresses 
are  obtained  by  varying  the  stroke  of  P. 

Wbhler's  Tension  Alternating  Stress  Machine. — Fig.  107 
shows  in  diagrammatic  outline  the  machine  used  by  Wohler  in 
his  tension  alternating  stress  experiments.  The  specimen  A 
is  held  in  suitable  shackles  B  and  C.  The  low  shackle  C  is 
made  of  adjustable  height  by  means  of  a  screwed  tail  rod, 
which  can  be  fixed  in  different  positions  relative  to  the  frame 
of  the  machine  by  means  of  the  nuts  shown.  The  upper 
shackle  B  is  carried  on  knife-edges  on  the  end  of  a  beam  C, 
which  is  supported,  also  on  knife-edges,  at  D.  Q  is  a  vertical 
oscillating  connecting  rod,  and  by  means  of  a  slot  and  pin  can 
be  made  to  give  a  variable  oscillating  stroke  to  the  lever  E. 
The  end  of  the  lever  C  carries  a  link  attached  to  the  horizontal 
beam  J,  whose  other  end  is  connected  to  a  similar  lever  and 
spring  used  in  the  torsional  machine.  The  oscillations  of  the 
lever  E  are  transmitted  by  means  of  a  pin  working  in  a  slot 
F  to  the  spring  H,  which  consequently  transmits  a  varying 
downward  pull  on  the  lever  J,  and  hence  causes  a  variable 
stress  on  the  specimen  A.  It  is  obvious  that  the  pull  on  the 
specimen  is  proportionate  to  the  tension  of  the  spring  L 
necessary  to  keep  the  lever  K  from  rising. 

To  set  the  machine  for  giving  a  stress  alternating  between 
two  fixed  limits,  the  spring  L  is  adjusted  by  means  of  the  nut 
M,  so  that  the  minimum  stress  would  make  the  lever  K  rise. 


ALTERNATING  STRESS  TESTS 


171 


172 


A  HANDBOOK  OF  TESTING  MATERIALS 


The  nut  P  and  the  right-  and  left-handed  coupling  nut  G  are 
then  adjusted  so  that  K  is  just  lifted. 

The  spring  L  is  now  set  to  give  the  maximum  stress,  and  the 
stroke  of  the  lever  E  adjusted  until  the  maximum  stress  just 
raises  the  lever  K.  All  is  now  ready  for  a  test. 

Wohler's  Bending  Stress  Machines. — Wohler  designed  two 
machines  for  testing  specimens  with  an  alternating  bending 
stress.  One  shown  diagrummatically  in  Fig.  108  is  arranged  for 
varying  the  stress  between  a  fixed  maximum  and  minimum, 


FIG.  108.  —  Wohler's  Variable  Bending  Stress  Machine. 

while  that  shown  in  Fig.  109  bends  the  specimen  rapidly  in 
opposite  directions,  so  that  at  any  particular  point  the  stress 
alternates  between  a  compressive  and  tensile  stress  of  equal 
intensity. 

Eeferring  to  Fig.  108,  A  is  the  specimen  (a  beam)  supported 
on  knife-edges  at  1)  and  E.  One  of  these  latter  I)  is  fixed, 
while  the  other  E  is  attached  by  a  link  to  the  same  lever  and 
spring  arrangement  which  we  have  seen  in  the  other  alternat- 
ing stress  machines.  The  load  is  applied  through  the  usual 
oscillating  connecting  rod  and  lever  B  to  the  knife-edge  M. 
The  lever  B  is  attached  to  the  vertical  rod  K  by  a  pin  working 
in  a  seat,  so  that  no  upward  push  can  be  given  to  the  beam. 


ALTERNATING  STEESS  TESTS 


173 


To  set  the  machine  for  a  required  variation,  the  spring  G  is 
adjusted  by  the  nut  L  to  such  a  load  that  the  beam  F  is  lifted 
by  the  minimum  load  to  be  applied  to  the  beam.  The  screw 
J,  which  is  rigidly  held  by  the  fixed  cross-beam  H,  is  then 
screwed  down  until  F  justs  lifts.  G  is  now  tightened  up  by 
the  nut  L  to  the  maximum  load,  and  the  stroke  of  the  lever  B 
adjusted  until  the  lever  F  is  just  lifted  at  the  end  of  the  stroke. 
All  is  now  ready  for  a  test.  Adjustments  in  the  length  of  K 
can  be  made  by  means  of  a  turn-buckle,  while  the  stroke  of  B 


PIG.  109.— Wohler's  Machine  for  Eepeat  Bending  in  opposite  directions. 

is  varied  by  moving  the  attachment  pin  on  C  along  a  slotted 
link. 

In  the  second  bending  stress  machine  shown  in  Fig.  109  two 
specimens  are  used,  A  and  AI;  these  are  fixed  by  driving  into 
two  chucks  placed  at  either  end  of  a  mandril  C,  running  in 
bearings  D  and  DI,  and  carrying  a  pulley  B.  The  specimens 
are  first  turned  in  a  lathe,  so  that  they  shall  be  perfectly 
straight,  and  then  bearings  are  attached  to  them  at  E  and  EI 
of  such  a  kind  that  a  downward  pull  can  be  exerted  at  these 
points  by  means  of  two  spring  balances  F  and  FI.  The  pull  of 
these,  which  were  of  a  special  kind,  shown  diagrammatically  in 
the  figure,  could  be  varied  by  adjusting  the  nuts  at  G  and  Gi. 
It  is  obvious  that  when  the  pulley  B  is  rotated  the  specimens 
will  be  subjected  to  a  bending  which  is  equivalent  to  being 


174 


A  HANDBOOK  OF  TESTING  MATERIALS 


rapidly  bent  backwards  and  forwards  in  opposite  directions. 
The  load,  in  fact,  is  similar  to  that  acting  on  the  axles  of  a 
railway  coach  when  running. 


TABLE  XIY. — WOHLER'S  EXPERIMENTS  ON  BARS  SUBJECTED  TO 
REPETITIONS  OF  TRANSVERSE  STRESS  (ROTATING  BARS) 
BETWEEN  EQUAL  AND  OPPOSITE  LIMITS  OF  STRESS. 

SET  I. 


No.  of 
Bar. 

Material. 

Stress  applied  in  tons 
per  sq.  in. 

Range  of  Stress 
in  tons  per  sq.  in. 

No.  of  Repetitions 
before  Fracture. 

Maximum. 

Minimum. 

1 

1 

+  15-3 

-15-3 

30-6 

56,430 

2 

14-3 

14-3 

28-6 

99,000 

3 

13-4 

13-4 

26-8 

183,145 

4 

Iron  for 

12-4 

12-4 

24-8 

479,490 

5 

axles, 

11-5 

11-5 

23-0 

909,840 

6 

Phoenix  Co. 

10-5 

10-5 

21-0 

3,632,588 

7 

9-6 

9-6 

19-2 

4.917,992 

8 

8-6 

8-6 

17-2 

19,186,791 

9 

7-6 

7'6 

15-2 

132,250,000! 

SET  II, 


24 

+23-9 

-23-9 

47-8 

2,375 

25 

22-9 

22-9 

45-8 

4,986 

26 

21-9 

21-9 

43-8 

11,636 

27 

Homo- 

18-2 

18-2 

36-4 

31,586 

28 

geneous 

16-3 

16-3 

32-6 

94,311 

29 

iron. 

14-3 

14-3 

28-6 

161,262 

30 

13-4 

13-4 

26-8 

464,786 

31 

12-4 

12-4 

24-8 

636,500 

32 

11-5 

11-5 

23-0 

3,930,150 

SET  III. 

33 

. 

+20-1 

-20-1 

40-2 

55,100 

34 

17-2 

17-2 

34-4 

127,775 

35 
36 
37 

38 

Krupp's 
-    cast-steel    - 
axles. 

16-3 
15-3 
15-3 
15-3 

16-3 
15-3 
15-3 
15-3 

32-6 
30-6 
30-6 
30-6 

797,525 
642,675 
1,  665,5*0 
3,114,160 

39 

H-3 

14-3 

28-6 

4,163,375 

40 

'                         * 

14-3 

14-3 

28-6 

45,050,640 

1  Not  broken. 


ALTERNATING  STRESS  TESTS 


175 


Fig.  110  shows  the  nature  of  the  stress-cycle  in  Wohler's 
machine  (Fig.  109).     In  the  diagram  are  marked  the  points  of 
maximum  skin  stress — tension  and  compression,  or  +  and— 
viz.,   MTS   and   MCS.     At    Z 
and    Z1,   the   stress   is   zero. 
Prof.   Arnold l    (in    a    paper 
from  which   the    author   has 
obtained  much  of  the  follow- 
ing information)  quotes  three 
sets  of  Wohler's  tests  (p.  174). 
The   first   set    has   reference 
to   wrought-iron   of    average 
statical  maximum  stress,  21*3 
tons  per  sq.  in. ;  the  second 
set,      on      material      called 


FlG.  110. — Diagram  showing  nature 
and  Stress-Cycle  of  the  Wohler 
Test. 


"  homogeneous  iron,"  was  probably  mild  steel,  or  ingot  iron, 
having  a  mean  maximum  stress  of  28'2  tons  per  sq.  in.     The 
third  set  was  probably  made  upon  crucible  steel  of  0*6  per  cent, 
carbonj  with  a  mean  maximum  stress  of  46'4  tons  per  sq.  in. 
Arnold's   Machine. — Prof.   Arnold   conceived  the   idea   of 

bringing  Wohler's 
method  into  practical 
works  use  by  greatly 
reducing  the  time 
occupied  in  making  a 
test.  He  proposed  to 
stress  the  material  just 
beyond  its  elastic  limit, 
and  so  reduce  the  time 


MT? 
/ 


Z-\ 


taken  to  make  a  test 
from  hours  to  seconds. 
In  Fig.  Ill  the  nature 
of  Arnold's  test  is 
shown.  B  is  the  test 
piece,  |  inch  diameter  and  about  6  inches  long.  It  is  gripped  in 
the  dieD,  and  the  stress  is  applied  by  the  strokes  of  the  slotted 

1  Trans.  Inst.  N.  A.,  1909 


FIG.  111. — Diagram  showing  Nature  and 
Stress-Strain  Lines  in  Arnold's  Test. 


176 


A  HANDBOOK  OF  TESTING  MATERIALS 


plunger  PP.  A  rate  of  alternation  of  650  per  minute  is  adopted. 
The  diagrams  show  the  alternation  of  the  stress-strain  lines  in 
this  test.  Z  is  the  fixed  zero  of  stress.  Theoretically  the  Wohler 
test  is  perfect,  while  Prof.  Arnold's  is  wrong;  but  never- 
theless it  gives  valuable  results  concerning  properties  which 
Wohler's  tests  do  not  reveal.  No  matter  how  dangerously 
brittle  steel  may  be,  from  chemical  or  physical  causes,  if  such 
treatment  has  produced  a  high  elastic  limit,  the  Wohler  test 
shows  the  material  safe  if  stressed  well  short  of  that  limit. 
As  a  matter  of  fact,  such  steel  suddenly  ruptures,  sooner  or 
later,  under  stresses  theoretically  quite  safe.  As  an  instance  of 
this,  results  of  some  tests  made  on  several  steels  by  Mr.  J.  E. 
Stead,  F.R.S.,  are  given.  There  was  a  series  of  three  sets  with 
ascending  phosphorus  up  to  0'5  per  cent. — the  last-named 
being  most  undesirable  for  engine  parts.  The  analysis  showed 
everything  as  being  practically  identical,  except  the  phos- 
phorus, which  varies  as  shown  in  the  table  giving  the  results 
of  static  tests. 

TABLE  XV.— EESULTS  OF  STATIC  TESTS. 


Steel 
No. 

Phosphorus. 
Per  cent. 

Yield  Point. 
Tons  per  sq.  in. 

Maximum  Stress. 
Tons  per  sq.  in. 

Elongation.  Per 
cent,  on  6  ins. 

Reduction  of 
Area.     Per  cent. 

1 

•041 

20-4 

33-1 

23-0 

52-0 

2 

•302 

25-4 

39-9 

23-0 

45-3 

3 

•509 

32-0 

44-0 

20-0 

45-3 

The  Wohler  tests  made  by  Mr.  Stead  give  the  results  set 
forth  in  the  table  below,  the  stresses  being  +  and  —  15  tons 
per  sq.  in.,  i.e.,  a  range  of  30  tons. 

TABLE  XVI.— EESULTS  OF  WOHLER  TESTS. 


Steel  No. 

Phosphorus. 
Per  cent. 

Reversals  of  Stress 
endured. 

Ratio  of  Resistance  to 
Alternating  Stress. 

1 
2 
3 

•041 
•302 
•509 

61,000 
167,300 
651,000 

1-0 
2-7 
10-6 

ALTERNATING  STRESS  TESTS 


17 


Prof.  Arnold's  tests — made  by  him  at  Sheffield  University 
in  complete  ignorance  of  the  nature  of  the  steels — registered 
the  figures  embodied  in  the  table  below  : — 

TABLE  XVII.— PROF.  ARNOLD'S  ALTERNATING  STRESS  TESTS. 


Steel 
No. 

Phosphorus. 
Per  cent. 

Alternations  endured  in  Test  No. 
(Under  standard  conditions.) 

Ratio  of 
Resistance  to 
Alternating 
Stress. 

1. 

O4 

Mean. 

1 
2 
3 

•041 
•302 
•509 

258 
188 
72 

284 
212 

128 

272 

200 
100 

100 
37 

Speaking  in  round  numbers,  the  Wohler  test  indicated  that 
a  mild  steel  containing  0'5  per  cent,  phosphorus  was,  with 
equal  stresses,  ten  times  as  capable  of  resisting  alternating 
stress  as  a  steel  containing  0'04  per  cent,  phosphorus.  Prof. 
Arnold's  test,  on  the  other  hand,  indicated  that  a  steel  con- 
taining 0*5  per  cent,  phosphorus  had  about  one-third  the 
endurance  of  a  steel  containing  0'04  phosphorus.  The  curves 
of  the  yield  points  of  the  two  alternating  tests  of  the  three 
steels  show  that  the  Wohler  curve  is  similar  in  type  to 
that  registered  by  the  yield  point  or  apparent  elastic  limit, 
Professor  Arnold's  curve  being  in  an  opposite  direction  and 
indicating  what  is  well  known  to  be  the  mechanical  effect  of 
phosphorus  on  steel. 

The  evidence  supplied  above  seems  to  show  that  for  prac- 
tical purposes  Prof.  Arnold's  test  is  the  more  useful. 

Stanton's  Alternating- Stress  Testing  Machine. — The  prin- 
ciple of  this  machine  is  that  of  employing  a  rotating  crank 
to  cause  periodic  motion  of  a  reciprocating  mass  by  means  of 
a  connecting  rod,  the  specimen  under  test  forming  the  con- 
nection between  the  reciprocating  mass  and  the  crosshead. 
This  device  has  been  employed  by  Prof.  Osborne  Eeynoids  in 
the  testing  machine  at  Owens  College,  which  is  of  the  vertical 
liype  with  a  single  balanced  crank.  In  the  National  Physical 
Laboratory  machine  there  are  four  cranks  operating  four 

T.M.  N 


178  A  HANDBOOK  OF  TESTING  MATEEIALS 

specimens,  the  motion  of  the  specimens  being  in  a  horizontal 
plane.  By  this  means  the  balancing  of  the  machine  is  made 
independent  of  the  ratio  of  the  crank-arm  to  the  connecting 
rod,  so  that  a  length  of  crank-arm  has  been  adopted  which 
enables  experiments  to  be  made  at  moderately  low  speeds, 
that  is,  from  600  to  1,000  revolutions  per  minute.  Although 
this  arrangement  causes  the  motion  of  the  specimens  to 
deviate  from  the  simple  harmonic  law,  the  effects  on  the 
stresses  set  up  in  the  specimens  are  sufficiently  small  in 
value  to  be  neglected,  so  that  the  maximum  tensile  force  on 
the  specimens  may  be  taken  as 


and  the  maximum  compressive  force  on  the  specimens  as 


where  W  =  weight  of  mass  attached  to  end  of  specimen  in 
Ibs.  ; 

r  =  radius  of  crank  pin  ; 
ic  =  mean  angular  velocity  of  crank-shaft  ; 
I  =  length  of  the  connecting  rod. 

It  will  be  observed  that  the  maximum  tensile  stress  is 
1*4  times  the  value  of  the  maximum  compressive  stress, 
which  is  approximately  the  ratio  of  the  stresses  in  the 
piston-rod  of  an  ordinary  reciprocating  steam  engine.  The 
form  of  specimen  adopted  is  the  same  as  in  Eeynolds  and 
Smith's  experiments,  consisting  of  a  5-  inch  bar  screw  cut 
^3T-inch  Whit  worth,  and  turned  down  in  the  centre  to  a 
diameter  of  J  inch  for  a  length  of  J  inch.  Great  care 
has  to  be  taken  in  the  preparation  of  the  specimens  to 
ensure  a  gradual  change  of  section  in  the  turned-down  part, 
as  the  effect  of  a  change  of  section  on  the  resistance  of  the 
specimen  is  much  more  marked  in  the  case  of  tests  under 
alternating  stresses  than  in  statical  tests. 

Prof.  J.  H.  Smith's  Alternating  Tension  and  Com- 
pression Stress  Machine.1  —  This  machine,  called  by  its 

1  Engineering,  Vol.  LXXXVIIL,  p.  105. 


ALTERNATING  STRESS  TESTS 


179 


inventor  a  fatigue  testing  machine,  was  designed  by  Dr.  J.  H. 
Smith  in  1904,  but  subsequently  modified  to  its  present  form. 
In  this  machine,  as  in  Stanton's,  the  load  is  produced  by  the 
centrifugal  force  of  a  rotating  mass.  Fig.  112  shows  the 
general  scheme  of  the  apparatus  employed.  If  we  have  two 
masses  fixed  to  the  ends  of  revolving  arms  which  are  pivoted 
at  A  and  B,  it  is  obvious  that  when  the  weights  are  at  the  top 


FIG.  112. — Diagram  of  J.  H.  Smith's  Alternating  Stress  Machine. 

of  their  motion  they  will  pull  the  arm  AB  upwards  with  a 
force  expressed  by  the  usual  formula 

2WV'2 
gr 

If  now  AB  is  rigidly  attached  to  a  vertical  spindle  passing 
through  guides  at  C  and  D,  and  if  we  place  a  specimen  F 
between  the  end  of  the  spindle  and  a  fixed  mass  E,  then  the 
specimen  will  be  subjected  to  the  force  expressed  above  in 
compression.  When  the  weights  are  at  the  bottom  of  their 
revolution  the  force  on  the  specimen  will  be  reversed.  Suppose 
now  we  attach  a  spring  H  to  the  bottom  of  the  spindle  and 

N  2 


180  A  HANDBOOK  OF  TESTING  MATERIALS 

tighten  this  up  so  as  to  exert  a  force  of  S  Ibs.  weight.     Then 
the  load  on  the  specimen  will  vary  between 


, 
—  S  and  -         -fS. 


fir 

By  making  S  greater  than 

2WV* 
gr 

the  load  on  the  specimen  is  always  tensile. 

In  the  latest  form  of  apparatus  used  by  Dr.  Smith,  the 
apparatus  is  double,  two  specimens  being  under  test  at  one 


FIG.  113.— Diagram  of  J.  II.  Smith's  Alternating  Stress  Machine. 

time.  Fig.  113  shows  this  arrangement,  and  it  will  be  observed 
how  two  other  masses  are  introduced  for  the  purpose  of 
balancing.  P  is  a  pulley,  and  C  a  counter.  The  specimens 
generally  used  are  small,  being  only  J  inch  in  diameter  and 
|  inch  long,  but  by  introducing  a  special  form  of  chuck 
lengths  up  to  4  inches  can  be  used. 

Fig.  114  gives  an  idea  of  the  scheme  as  actually  carried  out 
in  practice.  The  part  shown  is,  as  was  explained  previously, 
duplicated,  and  the  whole  machine  runs  in  an  oil  bath. 
Eef erring  to  Fig.  114,  there  is,  of  course,  no  rigid  connection 
at  the  point  A,  the  arrangement  consisting  of  a  small  slider 
working  in  guides.  Otherwise  part  of  the  forces  due  to  the 


ALTERNATING  STRESS  TESTS 


181 


revolving    weights    would     be    taken    up     by    the    driving 
shaft. 

The    reader   is  referred    to    the    article    in    Engineerinq, 


(*) 


FIG.  114.— J.  II.  Smith's  Alternating  Stress  Machine. 

mentioned  previously,  for  a  full  description,  together  with 
particulars  of  the  very  ingenious  optical  strain  recorder  and 
stress-strain  oscillograph  used. 


182 


A  HANDBOOK  OF  TESTING  MATERIALS 


The  following  are  some  results  obtained  by  Dr.  Smith  on 
this  type  of  machine  :— 

TABLE  XVIII. 
Oscillatory  weight,  12-42  Ibs.     Diameter  of  specimen,  -2409  inch. 


Set  A. 
Mild  Steel. 

Revolutions 
per  minute. 

Maximum  or 
Tensile 
Stress  per 
sq.  in. 

Minimum  or 
Compression 
Stress  per 
sq.  in. 

Range  of 
Stress  per 
Sq.  ill. 

Number  of 
Reversals 
before 
Rupture. 

Tons. 

Tons. 

Tons. 

Annealed    . 
Unannealed 

2,126 
2,122 

7-99 
8-03 

7-11 
7-17 

15-1 
15-2 

248,700 
226,500 

A  Ring-Shaped  Specimen.— Dr.  Stanton  has  very  ingeni- 
ously devised  an  apparatus  in  which  the  specimen  used  is  a 
ring.  The  latest  annual  report  (1910)  from  the  National 
Physical  Laboratory  contains  an  account  of  some  high, 
frequency  experiments.  The  number  of  reversals  has  been 
2,200  per  minute,  and  the  results  are  very  satisfactory  for 
hard  steels  (above  3  per  cent,  carbon).  In  the  case  of  the 
softer  steels  and  iron,  indentations  which  weaken  the  ring 
occur.  Dr.  Stanton  has  successfully  checked  the  results  from 
his  ring  method  against  tests  made  with  a  Wohler  machine 
running  at  the  same  frequency.  Dr.  Stanton  adheres  to  the 
opinion  that  the  range  of  stress  is  not  altered  by  the  speed, 
and  that  neither  iron  nor  high -carbon  steel  are  worse  at  high 
speeds  than  low  speeds.  Dr.  Smith,  of  Belfast,  and  others 
are  opposed  to  this  opinion.  Since  various  independent 
investigators  are  at  work  on  the  subject  we  may  soon  hope 
for  a  definite  decision  and  numerical  data  on  the  effect  of 
frequency  upon  the  range. 

C.  A.  M.  Smith's  Alternating  Torsion  Machine.— Wohler 
and  other  investigators  have  designed  machines  to  work 
between  +  and  —  loads  as  already  described.  A  machine 
has  been  designed  by  the  author  to  do  the  same  type  of  work, 
but  the  alterations  are  produced  by  loading  a  shaft  so  that  a 
torque  is  applied.  The  principle  of  the  machine  is  the 


ALTEENATING  STEESS  TESTS 


183 


stopping  and  starting  of  a  fly-wheel.  The  power  is  supplied 
by  a  small  motor.  Experiments  have  not  yet  been  made 
with  the  apparatus,  which  is  still  in  the  course  of  construction. 
The  chief  practical  difficulties  appear  to  be  those  concerned 

Static  Breaking    + 


— h 


D 


007.  i 


0 


iz 


Mian 


oFZO 
F 


50 


2 


2 


Tear 


oF8 


30 


20 


Ten 


ion 


Zero 


St 


ress 


Con  ore: 


s/or 


9          / 


10 


20 


30 


4-0  C 


PIG.  115.— Curve  for  Eationalisation  of  Alternating  Stress  Experiments. 

with  obtaining  balance  so  that  there  shall  not  be  undue 
vibration  at  high  frequencies.  There  is  a  minor  difficulty  of 
securing  specimens  to  the  grips,  which  would  not  occur  but 
for  the  special  design — for  other  purposes — of  the  specimens 
used. 

Repeat  Stresses. — Prof.  Goodman  has  given  a  method  of 

determining  graphically  the  allowable  maximum  stress  for  a 


184  A  HANDBOOK  OF  TESTING  MATERIALS 

given  variation  of  stress,  the  statical  breaking  stress  being 
given.  Draw  two  ordinates  A  B  (Fig.  115),  C  D  set  off  0  D  to 
represent  the  statical  breaking  stress,  and  through  0  put  in 
through  E  F.  Then  if  H  k  is  the  minimum  stress  on  the 
member,  H  I  is  the  maximum  load  which  can  be  repeated 
0  E  at  45°  as  a  convenient  slope,  the  horizontal  scale  being 
immaterial.  Bisect  0  D  and  join  indefinitely  without 
breaking  the  bar.  The  stress  scale  is  marked  in  per- 
centage of  the  static  breaking  load.  The  points  indicate 
the  results  of  experiments  by  Wohler,  Spangenberg,  and 
Bauschinger,  and  it  will  be  observed  that  theory  and 
experiment  coincide  as  closely  as  can  reasonably  be 
expected.  Expressed  algebraically  we  have,  when  designing 
a  member  which  will  be  subjected  to  both  a  steady  load  Wmin. 
and  a  fluctuating  load  (Wmax.  —  Wmin.),  the  equivalent  static 
load.  * 

W0  =  Wmin:  +  2  (Wmax.  -  Wmin.) 

The  plus  is  used  when  both  the  loads  act  together,  i.e.,  when 
both  are  tension  or  both  compression,  and  the  minus  when 
they  act  against  one  another. 

Sankey's  Hand  Bending  Machine. — This  machine  has  been 
specially  designed  for  the  rapid  testing  of  material,  and  is  in 
a  convenient  form  for  use  in  works. 

The  principle  on  which  it  is  based  is  to  bend  the  test  piece 
backwards  and  forwards  until  it  is  broken,  the  bending  effort 
being  measured  by  the  deflection  of  a  spring.  A  device  is 
fitted  for  automatically  recording  not  only  this  bending  effort 
for  each  bend,  but  also  the  number  of  times  the  specimen  can 
be  bent  without  rupture,  as  well  as  the  total  energy  required 
to  break  it.  A  diagram  is  obtained,  the  form  of  which  shows 
at  a  glance  the  quality  of  the  material. 

The  machine  gives  most  of  the  information  needed  in  the 
workshop  as  regards  the  strength  of  the  material  in  respect 
of  static  stresses,  and  hence  compares  not  unfavourably  with 
the  more  lengthy  and  expensive  tensile  tests  ;  but,  in  addition, 
it  exhibits  in  a  striking  manner  what,  for  want  of  a  better 


ALTEENATING  STEESS  TESTS 


185 


word,  may  be  called  the  "  leatheriness  "  of  the  material,  or, 
in  other  words,  its  power  to  resist  the  effect  of  alternations  of 
stress,  that  is  to  say,  "  fatigue." 

One  bend  is  denned  as  bending  the  test  piece  from  the 
extreme  position  on  the  right  to  the  extreme  position  on  the 
left,  or  from  the  extreme  position  on  the  left  to  the  extreme 
position  on  the  right. 

The  machine  is  illustrated  in  Fig.  116,  and  consists  of  a  small 
bed-plate,  arranged  to  bolt  down  to  a  bench,  at  one  corner  of 


FIG.  116. — Sankey's  Hand  Bending  Machine. 

which  there  is  a  grip  A  for  securing  one  end  of  a  flat  steel  spring 
B.  The  other  end  of  the  spring  is  fitted  with  a  special  grip  C 
for  holding  one  end  of  the  test  piece  D.  The  other  end  of  the 
test  piece  is  fixed  into  a  handle  E,  about  3  feet  long,  by  means 
of  which  it  is  bent  backwards  and  forwards  through  the 
"  standard  "~  angle.  An  indicator  F  is  provided  to  show  this 
standard  angle.  Alongside  of  the  spring,  and  fixed  to  the  bed- 
plate, there  is  a  horizontal  drum  G  to  carry  the  recording 
paper,  and  the  pencil  H  has  a  horizontal  motion  actuated  by  the 
motion  of  the  grip  C  and  conveyed  by  the  steel  wires  L  and  M 
and  the  multiplying  pulley  N,  the  wires  being  kept  taut  by  the 
spring  box  0.  The  zero  line  is  in  the  middle  of  the  paper, 
and  the  pencil  H  moves  in  one  direction  when  the  bending 


186 


A  HANDBOOK  OF  TESTING  MATEEIALS 


is  from  right  to  left,  and  in  the  opposite  direction  when  it  is 
from  left  to  right.  The  drum  has  a  ratchet  wheel  K  with  a 
detent  (not  shown)  worked  by  the  motion  of  the  pencil 
carrier.  The  result  of  the  combined  motion  of  the  pencil 
and  of  the  drum  is  to  produce  an  autographic  diagram 
such  as  shown  in  Fig.  117.  Obviously  the  greater  the  stiff- 
ness of  the  test  piece  the  more  the  flat  spring  B  will  have  to 
be  bent  before  its  resistance  is  equal  to  the  resistance  to 
bending  of  the  test  piece.  Hence  the  motion  of  the  pencil 
is  proportional  to  the  effort  required  to  bend  the  test  piece. 

The  test  piece  is  properly  secured  in  the  handle  E  (Fig.  116) 
by  means  of  the  set  screw,  it  is  then  inserted  into  the  grip  C, 


j 


FIG.  117. — Autographic  Diagram  from  Hand-bending  Machine. 

and  the  free  length  (If  inches)  is  adjusted  by  means  of  a 
gauge  provided  for  the  purpose,  after  which  the  grip  C  is 
tightened.  The  first  bend  is  taken  to  the  left  until  the  mark 
on  the  handle  coincides  with  the  pointer  indicating  the 
"  standard  "  angle.  The  bending  is  then  reversed,  and  the 
test  piece  is  bent  until  the  mark  on  the  handle  coincides  with 
the  second  pointer.  The  bending  is  again  reversed,  and  so  on 
until  the  specimen  breaks.  The  point  at  which  the  test  piece 
breaks  should  be  noted  in  decimals  of  one  bend,  which  are 
marked  on  the  indicator. 

The  "  standard  "  angle  is  so  fixed  that  the  distance  travelled 
along  the  arc  of  the  circle  1  foot  radius  from  the  point  of 
bending  the  test  piece  is  1*60  ft.  (this  angle  is  91|°). 
Hence  by  multiplying  the  bending  effort  (in  Ibs.)  by  1/6  the 
energy  (in  ft.  Ibs.)  required  to  make  a  complete  bend  is  found. 


ALTERNATING  STRESS  TESTS  187 

Generally,  the  stronger  the  material  the  less  the  number  of 
bends  it  will  endure,  and  approximately  it  may  be  taken  that, 
in  the  case  of  mild  steel,  the  bending  effort  of  the  first  bend 
is  proportional  to  the  yield  stress  in  tension  of  the  material. 
It  has  been  found  by  experience  that  with  the  standard  test 
piece  (f  inch  diameter),  one  half  of  the  bending  effort  in 
ft.  Ibs.  is  nearly  equal  to  the  yield  stress  in  tons  per 
sq.  in.  This  rule  is  only  approximate,  but  it  will  give  a 
fair  idea  of  the  strength  of  the  material  as  expressed  in  the 
.ordinary  way.  The  number  of  bends  is  proportional  to  the 
ductility  of  the  material,  and  experiment  shows  that  this 
number  is  approximately  proportional  to  the  elongation 
multiplied  by  the  reduction  of  area  in  a  tensile  test. 

The  area  of  the  autographic  diagram  represents  the  energy 
required  to  break  the  test  piece.  The  recording  gear  has 
been  so  proportioned  that  1  sq.  in.  of  this  diagram  is  equiva- 
lent to  400  ft.  Ibs.  The  area  in  question  can  be  obtained  by 
means  of  a  planimeter,  but  it  can  also  be  approximately 
arrived  at  by  estimating  the  average  bending  effort,  and  multi- 
plying by  1/6  times  the  number  of  bends.  1/6  times  the 
number  of  bends  must  be  taken,  because,  as  already  pointed 
out,  the  arc  swept  by  the  point  of  application  of  the  bending 
effort  (in  ft.  Ibs.)  is  1/60  foot  for  each  bend.  This  energy 
figure  gives  valuable  information  as  to  the  quality  of 
the  material,  and  for  machinery  steel  should  not  be  less 
than  2,500  ft.  Ibs.,  but  for  the  steel  used  in  petrol  engines 
and  the  like  a  higher  figure  is  desirable,  say  3,500  to  4,000 
ft.  Ibs. 

Many  trials  show  that  with  steel  in  a  normal  condition 
the  first  bending  effort  is  always  distinctly  less  than  the 
second  bending  effort  (see  Fig.  117).  But  if  the  steel 
has  been  artificially  stiffened  by  drawing  or  hammering, 
the  first  bending  effort  is  the  greatest  (see  Fig.  117).  In 
fact,  the  effect  of  the  bending  is  to  undo  the  artificial 
stiffening.  This  is  a  valuable  and  unique  property  of  this 
testing  machine. 

Fractures. — The  following  is  a  short  list  of  the  fractures, 


188  A  HANDBOOK  OF  TESTING  MATEEIALS 

with  this  machine,  obtained  with  steels  of  good  quality,  and 
the  probable  inferences  to  be  drawn  therefrom : — 

FRACTURES.  PROBABLE  INFERENCES. 

Silky         "...         Mild  steel,  nickel  steel. 

Granular    ...•         ...          ...     Medium  carbon  steel. 

Fine  crystalline    ...          ...     High  carbon  steel. 

Granular  and  crystalline  . . .  Mild  and  medium  carbon 

steels  when  overheated. 

Coarse  crystalline...          ...     Mild   and    medium    carbon 

steels  when  overheated, 
and  then  hammered  at  too 
low  a  temperature. 

Effect  of  Speed. — Some  interesting  results  have  been 
obtained  by  Mr.  E.  M.  Eden1  on  a  machine  of  the  rotating 
beam  type,  in  which  the  specimen  is  subjected  to  a  bending 
moment  and  no  shear.  Five  materials  were  tested  at  speeds 
of  about  300,  600  and  1,300  v.p.m.  Within  the  range  of  the 
experiments  the  endurance  is  independent  of  the  speed  at 
which  the  machine  is  run.  The  apparatus  is  comparatively 
simple  and  seems  suitable  for  college  laboratories.  The  dis- 
agreement of  various  experimenters  using  different  methods 
of  obtaining  alternating  stress  shows  that  the  subject  is  not  yet 
exhausted.  Work  has  also  been  done  by  Bairstow 2  and 
Howard.3 


1  Univ.  of  Durham  Phil.  Soc.,Proc.  1909—10. 

2  Phil.  Trans.  Royal  Society,  December,  1909. 

:i  International  Association  for  Testing  Materials,  1909. 


CHAPTER  X 

THE    TESTING    OF    CEMENTS,    REINFORCED     CONCRETE,    AND     STONES 

AFTER  mild  steel,  the  above  are  probably  the  most  im- 
portant materials  of  construction ;  all  of  them  are  very  variable 
in  their  properties,  and  much  depends  on  the  method  of 
testing.  In  the  case  of  Portland  cement  we  have  given  an 
outline  of  the  methods  laid  down  by  the  Engineering 
Standards  Committee,  and  as  so  much  depends  on  method, 
it  is  important  to  follow  this  method  as  closely  as  possible 
where  comparative  results  are  desired.  It  will  be  noted  that 
even  the  rate  of  loading  may  considerably  affect  the  results. 
Table  21  gives  an  idea  of  results  obtained  at  different  rates  of 
loading. 

In  the  case  of  reinforced  concrete,  only  those  results 
obtained  on  full  size  constructional  members  or  pieces  of 
work  can  be  considered  as  giving  reliable  results,  hence  we 
have  refrained  from  giving  results  of  tests  except  such  as  give 
what  may  be  considered  the  fundamental  properties,  i.e.,  the 
co-efficient  of  elasticity,  the  adhesive  force  of  iron  bars,  and 
the  crushing  strength,  together  with  an  account  of  a  full 
size  test  on  a  floor. 

THE  TESTING  OF  CEMENTS  AND  CONCRETES. 

The  standard  method  of  testing  Portland  cement  is  laid 
down  by  trie  British  Engineering  Standards  Committee ]  as 
follows  : — 

Fineness  and  Sieves. — The  cement  shall  be  ground  to 
comply  with  the  following  degrees  of  fineness,  viz. : — 

Residue  on  sieve  76  X  76  meshes  per  sq.  in.  not  to 
exceed  3  per  cent. 

1  The  Committee's  actual  specification  (Report  No.  12.  Revised  August, 
1910  British  Standand  Specification  for  Portland  Cement)  should  be  consulted 
for  tests  intended  to  comply  in  detail  with  their  recommendations. 


190 


A  HANDBOOK  OF  TESTING  MATERIALS 


•  X--0-  06  approximately 

0  10'approximattly 


3  00' 


Eesidue  on  sieve  180  X  180  meshes  per  sq.  in.  not  to  exceed 

18  per  cent.      [Sieves  as  per  British  Standard  Specification.] 

Specific  Gravity. — Not  less  than  3*15  when  fresh  burnt  and 

ground,  and  not  less  than  3*10  if  cement  has  been  ground 

for  not  less  than  four  weeks. 

Chemical   Composition. —  [See  British    Standard    Specifi- 
cation]. 

Mode  of  Gauging. — The  cement  shall  be  mixed  with  such  a 
proportion   of   water   that   after   filling   into  the  mould  the 
mixture  shall  be  plastic.    Fresh  water  to  be  used  at  a  tempera- 
ture between  58°  and  64°  F. 

DIMENSIONS  OF  BRIQUETTE  A  suitable   form   of    mould 

designed  to  give  a  form  of 
briquette  to  the  dimensions 
shown  in  Fig.  118  to  be  filled 
with  the  cement  without 
mechanical  ramming  and 
allowed  to  stand  on  a  non- 
porous  plate  until  the  cement 
sets.  As  soon  as  the  briq- 
uette can  be  removed  without 
injury,  this  should  be  done, 
and  the  briquette  kept  in  a 
damp  atmosphere  for  twenty- 
four  hours,  after  which  it 
should  be  kept  in  a  bath  of  clean  fresh  water  between  58°  and 
64°  F.,  and  allowed  to  remain  there  until  breaking,  the  water 
to  be  changed  every  seven  days. 

Testing. — Twelve  briquettes  should  be  prepared  for  each 
test — six  to  be  broken  after  seven  days,  and  six  after  twenty- 
eight  days.  The  usual  type  of  machine  for  testing  the  speci- 
mens is  described  below.  When  testing  with  standard  sand, 
the  latter  to  be  obtained  from  Leighton  Buzzard,  and  accord- 
ing to  the  British  Standard  Specification.  The  Committee  lay 
down  the  following  tensile  strengths  as  the  minimum  allowable. 
Neat  Test.— (Average  of  six  specimens.) 

7  days  from  gauging     .         .     400  Ibs.  per  sq.  in. 


FIG.  118. — Dimensions  of  Standard 
Briquette  (British  Standard  Speci- 
fication). 


CEMENTS,   EEINFOECED  CONCRETE,   AND  STONES     191 

Sand   Test. — (Average   of   six   specimens)   (3   parts   sand, 
1  cement.) 

7  days  from  gauging     .         .150  Ibs.  per  sq.  in. 
Setting  Time.— Cement  is  said  to  be  set  when  on  gently 


Weight  300  grammes 


FIG.  119. — Setting  Needle  for  Cement  (British  Engineering   Standards 
Committee's  suggestion). 

applying  the  "needle"  of  the  instrument  illustrated  in 
Fig.  119  no  impression  is  made  in  the  surface.  The  follow- 
ing times  of  setting  define  the  terms  slow,  medium,  and  quick 
setting  :— 

Quick.— Final  setting  time  not  less  than  10  nor  more  than 
30  minutes. 


192 


A  HANDBOOK  OF  TESTING  MATEEIALS 


Medium. — Final  setting  time  not  less  than  30  nor  more 

than  120  minutes. 
Slow. — Final  setting  time  not  less  than  120  no  more  than 

300  minutes. 

Soundness. — The  standard  method  of  testing  for  soundness 
is  by  means  of  what  is  known  as  the  "  Chatellier  test,"  using 
the  apparatus  illustrated  in  Fig.  120.  The  small  brass  mould 
is  filled  with  neat  cement  and  placed  in  a  bath  of  water  at  a 
temperature  of  58°  to  64°  F.  for  twenty-four  hours,  the  two 
open  ends  being  covered  with  glass  plates.  At  the  end  of  this 


Spring  Brass 
suitable  Metal  about 
m   in  thickness 


FIG.  120.— Le  Chatellier  Soundness  Testing  Instrument  (British  Standard 

Specification). 

time  the  distance  between  the  pointers  is  measured,  and  the 
mould  placed  in  water  at  58°  to  64°  F.  which  is  brought  to 
boiling  point  in  twenty-five  to  thirty  minutes  and  kept  boiling 
for  six  hours.  After  cooling,  the  distance  between  the  points  is 
again  measured.  This  distance  will  be  found  to  have  increased, 
and  it  is  laid  down  that  this  expansion  must  in  no  case  exceed 
10  millimetres  after  twenty-four  hours  aeration,  or,  if  the  above 
test  has  failed,  5  millimetres  after  seven  days  aeration. 

Cement  Testing  Machine. — The  simple  form  of  machine, 
shown  in  Fig.  121,  is  used  for  testing  cement  and  concrete  in 
tension.  As  the  strength  of  these  materials  in  this  direction 
is  very  small,  the  machine  used  is  of  a  correspondingly  small 
size,  and  is  much  simpler  than  those  used  for  testing  metallic 
specimens.  The  cement  is  first  moulded  into  the  form  of  a 
briquette,  such  as  is  shown  in  the  figure,  and  is  such  that  the 


CEMENTS,   EEINFOECED  CONCRETE,   AND  STONES     193 

smallest  section  of  the  specimen  is  1  inch  square.  The 
briquette  is  held  in  well-greased  jaws  of  the  form  shown  in 
Fig.  121.  The  lower  of  these  is  capable  of  being  moved  vertically 
by  means  of  a  hand-wheel  and  screw  which  are  not  shown  in 
the  diagram.  The  upper  jaw  is  connected  to  a  point  B  on 
the  lever  A  C,  whose  fulcrum  A  is  attached  to  the  frame  of 
the  machine  G.  The  outer  end  C  is  connected  by  a  rod  C  D 
to  the  short  arm  of  the  lever  D  F,  whose  fulcrum  is  at  E. 
The  length  of  C  D  is  made  adjustable  so  that  the  lever  D  F 
may  be  in  a  horizontal  position  at  the  beginning  of  the  test. 


FIG.  121. — Cement  Testing  Machine. 

The  load  is  applied  by  means  of  a  variable  weight  H  which 
is  fixed  to  the  end  F  of  the  lever  D  F.  In  one  type  of  this 
machine  the  weight  H  consists  of  an  iron  pan  into  which  lead 
shot  is  poured  at  a  constant  rate,  so  that  the  load  uniformly 
increases  by  100  Ibs.  in  every  12  seconds.  When  the  specimen 
breaks  the  pan  of  shot  drops  on  to  a  movable  lever  which  it 
depresses,  thereby  automatically  cutting  off  the  supply  of  shot. 
The  shot  is  then  weighed  and  the  strength  of  the  cement 
calculated  by  means  of  the  known  leverages  in  the  machine. 

The  Bailey  machine  for  cement  testing  has  only  a  single 
lever,  from  the  short  end  of  which  the  specimen  is  gripped  in 
the  same  way  as  in  the  machine  just  described.  The  long 
end,  however,  supports  a  long  cylindrical  vessel  into  which 
water  is  flowing  from  a  tank  above  the  lever  during  tests.  The 

T.M.  o 


194 


A  HANDBOOK  OF  TESTING  MATEEIALS 


load  is  thus  applied  as  before,  at  a  uniform  rate.  When  the 
specimen  breaks  the  downward  movement  of  the  long  arm  of 
the  lever  is  utilised  to  automatically  cut  off  the  supply  of  water. 
A  scale  is  provided  on  the  water  vessel,  and  is  so  divided  that 
the  height  of  water  in  the  vessel  gives  the  breaking  load  of  the 
specimen  as  a  direct  reading. 


FIG.  122. — Machine  for  Compression  Tests  of  Stones  and  Cements. 

Compression. — The  resistance  of  concrete  to  compression 
is  usually  determined  by  crushing  cubes  of  4,  6,  8,  or  12-inch 
sides  at  some  stated  age.  The  strength  per  sq.  in.  will 
in  general  decrease  with  the  size  of  the  cube.  The  crushing 
load  may  be  obtained  in  any  ordinary  testing  machine 
provided  with  compression  plates  or,  where  much  of  this 
class  of  work  has  to  be  done,  on  a  machine  specially  built  for 
cement  testing.  These  special  machines  in  general  consist  of 


CEMENTS,   EEINFOECED  CONCEETE,  AND  STONES     195 

an  ordinary  hydraulic  press,  but  worked  with  oil  or  glycerine, 
in  which  the  piston  friction  is  so  far  reduced  that  a  gauge 
attached  to  the  main  cylinder  may  be  made  to  read  the 
crushing  load  direct.  This  gauge  must  be  so  constructed 
that  after  the  material  fails  the  pointer  will  still  indicate 
the  maximum  pressure,  as  failure  generally  takes  place 
suddenly  and  without  previous  cracking  of  the  material. 
Messrs.  Bailey  make  such  machines,  capable  of  exerting  a 
crushing  load  of  12,  60,  and  150  tons  respectively.  It  is 
most  important  in  the  testing  of  cements,  concretes,  stones, 
etc.,  that  the  bedding  should  be  absolutely  even,  as  otherwise 
splitting  at  the  highest  corner  will  take  place.  To  ensure  this 
even  bedding  plaster  of  Paris  is  generally  used.  The  compression 
plates  are  first  cleaned  and  then  slightly  oiled.  A  thin  paste  of 
plaster  is  then  put  on  the  lower  plate  about  a  quarter  of  an  inch 
thick.  The  block  is  carefully  bedded  on  to  this  and  another 
quarter  of  an  inch  put  on  top  of  the  block.  A  small  amount  of 
pressure  is  then  applied,  and  the  machine  allowed  to  stand 
until  the  plaster  is  set,  say,  in  about  five  to  ten  minutes. 

Loading  should  be  applied  slowly  and  evenly  till  fracture 
occurs,  which  in  homogeneous  material  tends  to  take  place 
by  shear  at  45°,  thus  forming  cones  in  the  case  of  cylinders, 
or  pyramids  in  the  case  of  cubes. 

Both  the  tensile  and  compressive  strength  are  very  variable, 
especially  the  former.  The  chief  conditions  which  determine 
the  strength  are  :— 

1.  Proportion  of  ingredients. 

2.  Quality  of  ingredients. 

3.  Amount  of  water  used 

4.  The  method  and  amount  of  mixing. 

5.  Amount  of  consolidation  effected. 

6.  The  form  of  the  piece. 

7.  Atmospheric  conditions  during  hardening. 

8.  Time  after  gauging. 

9.  Manner  and  speed  of  applying  load. 

The  following  tables  of  experimental  results  will  illustrate 
the  effect  of  the  above  : — 

o  2 


196 


A  HANDBOOK  OF  TESTING  MATEEIALS 


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CEMENTS,   REINFORCED  CONCKETE,   AND  STONES     197 
TABLE  XX. — EFFECT  OF  TIME  WHEN  APPLYING  LOAD.' 


Rate  of  Applying 
Stress.     Pounds 

Tensile  Strength 
obtained.     Pounds 

per  Min. 

per  sq.  in. 

50 

400 

100 

415 

200 

430 

400 

450 

6,000 

493 

TABLE  XXI. 


Tensile  Strength.     Pounds  per 

sq.  in.  for  stress  applied  at 

Cement. 

Proportions. 

Age  of 
Briquettes. 

rate  of  pounds  per  minute. 

100 

300 

500 

700 

900 

Portland 

Neat  cement 

7  and  14  days 

453 

485 

521 

520 

528 

»> 

Ditto 

3  months 

— 

590 

617 

622 

640 

5  ) 

1—2 

3  months 

445 

467 

487 

507 

510 

Natural 

Neat  cement 

7  days 

150 

169 

186 

— 

202 

»» 

Ditto 

3  months 

309 

351 

363 

378 

390 

5» 

1-2 

3  months 

255 

299 

327 

329 

354 

TABLE  XXII. — EFFECT  OF  PROPORTION"  OF  SAND. 

H  and  E  are  two  samples  of  Portland  Cement. 

Sand  used,  Eiver  Sand,  "Point-aux-Pins." 


Tensile  Strength,  Ibs.  per  sq.  in. 

Parts  Sand  to  1 
Cement  by 
Weight. 

Proportionate 
Strength, 
Two  years  if 
1    2-100. 

6  Months. 

2  Years. 

H 

R 

II 

R 

Mean. 

2 

512 

504 

534 

548 

541 

100 

3 

390 

335 

363 

355 

359 

66 

4-09 

295 

261 

296 

288 

292 

54 

6 

175 

144 

191 

174 

182 

35 

8 

113 

96 

132 

132 

132 

24 

10 

64 

74 

104 

116 

110 

20 

1  The  rate  of  loading  specified  by  the  B.E.S.C.  for  testing  Portland  cement  is 
100  Ibs.  in  12  seconds,  i.e.,  500  Ibs.  per  minute. 


198 


A  HANDBOOK  OF  TESTING  MATEBIALS 


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CEMENTS,  EEINFOECED   CONCEETE,  AND  STONES     199 


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A  HANDBOOK  OF  TESTING  MATEEIALS 


The  Application  of  BrinelFs  Ball  Test  to  Cement  Testing. 

— La  Revue  de  Metallurgie  and  Le  Genie  Civil  have  recently 
published  articles  dealing  with  the  testing  of  cement  and 
concretes  of  all  kinds  by  means  of  Brinell's  Ball  test. 

A  rough  and  ready  method  of  a  similar  nature  has  long  been 


20 

19 

.18 

<u 


I'2 

V' 
i* 


\ 


V 


IS        20        25       30       35       40       45       50       55        60'      ffS       70        75 

Time     Since     Gauging     in     hours. 
FIG.  123.— Tests  on  Cement  with  Brinell's  Ball  Test. 

in  use  for  the  rapid  testing  of  cements  as  to  their  setting 
properties;  it  consists,  in  fact,  of  observing  how  long  the 
hardening  must  be  allowed  to  continue  before  it  becomes 
impossible  to  make  any  considerable  mark  on  the  surface  by 
pressing  on  the  sample  with  the  thumb ;  exerting  a  force  of 
perhaps  20  to  30  Ibs.  Such  a  method  has,  of  course,  no 
scientific  pretensions,  as  has  the  following  :— 

The  sample  is  prepared  with  a  smooth  surface  by  flattening 


CEMENTS,   REINFORCED   CONCRETE,  AND  STONES     201 

it  with  a  sheet  of  glass  while  it  is  in  the  mould.  The  exact 
dimensions  of  the  mould  do  not  appear  to  affect  the  result,  but 
it  is  essential  that  the  specimen  should  not  be  less  than  2  to 
2  J  times  the  depth  of  the  deepest  impression  likely  to  be  made, 
and  of  sufficient  surface  area  so  that  the  impression  does  not 
have  to  be  made  too  near  the  edge,  as  in  that  case  cracking  is 
likely  to  take  place,  or  otherwise  unsatisfactory  results 
obtained.  The  size  of  ball  suggested  as  giving  the  best  results 
is  3  centimetres  in  diameter,  and  is  pressed,  after  being 
slightly  wetted,  on  to  the  surface  partly  by  the  weight  of  the 
apparatus  itself  and  partly  by  adding  lead  discs.  From  1  to 
20  kilos.  (2*2  to  44*0  Ibs.  approximately)  is  the  total  load  used  for 
new  samples,  although  for  old  material  700  to  800  kilos.  (1,540 
to  1,760  Ibs.)  pressure  is  sometimes  necessary  for  very  hard 
specimens. 

The  load  having  been  applied  for  a  short  time,  say  nine  or 
ten  seconds,  the  apparatus  is  removed  and  the  spherical  area 
of  the  depression  measured.  This  latter  is  found  to  be  prac- 
tically proportional  to  the  weight  and  to  the  fifth  root  of  the 
radius  of  the  ball  employed. 

For  a  given  or  fixed  diameter  of  ball 

Weight  in  kilogrammes. 

C  (the  hardness  number)— 75— r — : — = ^ — 

bphencal  surface  in  sq.  cms. 

Or  for  different  size  balls 

C  5y'Radius= Constant. 

It  will  be  noted  that  the  latter  is  the  same  as  for  the  metals. 

It  is  obvious  that  cements  will  not  give  such  a  clear  impres- 
sion as  metals  do,  so  that  even  when  using  a  microscope  it  is 
found  difficult  to  obtain  very. reliable  readings  after  about  90 
days'  setting,  but  below  that  time  very  consistent  results  appear 
to  have  been  obtained. 

The  curves  in  Fig.  123  show  how  the  diameter  of  the  impres- 
sion varies  with  the  time  of  setting  with  a  constant  load. 
The  samples  were  two  hydraulic  limes  denoted  by  the  letters 
A  and  B. 


202 


A  HANDBOOK  OF  TESTING  MATEBIALS 


TESTS  IN  CONNECTION  WITH  KEINFORCED  CONCRETE. 

Determination  of  Young's  Modulus. 
TABLE  XXIV.—  EXPERIMENTS  BY  PROFESSOR  HATT 


Proportions  of  the  Concrete. 

Age, 
days. 

EC. 

Stress 
where 
Measured, 
Ibs.  per 
sq.  in. 

Crushing 
Stress,  Ibs. 
per  sq.  in. 

Cement. 

Sand. 

Broken 

Stone. 

Gravel. 

Cinders. 

1 

2 

4 

_ 

_ 

9 

4-70  XlO6 

750) 

' 

2,880 

1 

2 

4 

•  —  • 

— 

9 

3  -94  XlO6 

1,500  ) 

1 

2 

4 

— 

— 

14 

4-34  XlO6 

750) 

^ 

/ 

2,575 

1 

2 

4 

— 

— 

14 

3-68  XlO6 

1,500  ) 

1 

2 

— 

— 

4 

9 

5  -58  XlO5 

— 

495 

1 

2 

— 

— 

4 

9 

5-53  XlO5 

— 

595 

1 

2 

— 

— 

4 

7 

6  -30  XlO5 

— 

416 

1 

— 

— 

5 

— 

6 

2-09X106 

— 

1,185 

TABLE  XXV.— ADHESIVE  FORCE  ON  EODS  (HATT).1 


Diameter  of 
Rodin 
Inches. 

Age  of 
Specimen,  in 
Days. 

Depth  of 
Rodin 
Concrete. 

Adhesion  in  Ibs.  per  sq.  in.  in  Nominal  Surface. 

Maximum. 

Minimum. 

Mean. 

& 

32 

72 

735 

470 

636 

1 

35 

76 

780 

714 

756 

1  These  results  are  somewhat  higher  than  those  usually  obtained.  The 
following^-by  Prof.  Warren,  of  Sydney  University,  were  performed  with  prisms 
of  concrete  12  inches  long  and  4  x  4-inch  section.  Concrete  mixed  1  :3  and 
and  1:2:2  stone  being  broken  to  f  inch  gauge.  Bars  of  Bessemer  steel  |  inch 
diameter. 


CEMENTS,   KEINFOKCED  CONCRETE,   AND   STONES     203 
TABLE  XXVI. 


Composition. 

Description. 

Cement. 

Sand. 

Slaves. 

Water, 
per 
cent. 

Age  in 
Days. 

per  sq.  in.  of 
surface. 

Bars  with  natural  i 
skin  on. 
Hardened  in  air.    / 

1 
1 

1 
1 

3 
3 

2 

2 

2 
2 

12 
12 
10 

10 

45 
45 
45 
45 

216-5  \ 
221-0  f  Mean, 
184-5  (    198. 

170-0  ; 

Ears  cleaned  with  ( 

1 
1 

3 

3 

— 

12-5 
12-5 

45 
45 

118-0  \ 

72-0  (  Mean, 

emery  paper. 
Hardened  in  air.    r 

1 
1 

2 
2 

2 

2 

10 
10 

44 
44 

154-0  (    125. 

155  -o; 

Bars  cleaned  with  / 

1 

3 

12 

45 

154-0  \ 

emery  paper.       \ 
Hardened  in       j 

1 
1 

3 
2 

2 

12 
10 

45 
45 

191-0  (  Mean, 
204-0  (    185. 

water. 

1 

2 

2 

10 

45 

191-0  7 

The  Testing  of  Ferro- Concrete  Beams. — The  Amsler- 
Laffon  beam  testing  machine,  which  has  been  specially 
designed  for  the  cross-breaking  tests  on  beams,  is  illustrated  in 
outline  in  Fig.  124.  A  is  a  cylinder  in  which  fits  a  ram  B,  the 
accuracy  of  the  fitting  being  such  that  no  packing  is  required 
when  castor  oil  is  used  as  the  pressure  medium.  '  D  is  the 
beam  which  can  be  loaded  by  a  single  concentrated  load  or  in 
two  places,  as  shown  in  Fig.  124,  in  which  latter  case  the 
stress  distribution  approximates  to  that  obtained  with  a  uni- 
formly distributed  load.  The  length  of  the  beam  is  between 
the  bearings  at  G  and  H.  At  these  points  the  beam  is  held 
down  by  rods  which  pass  underground  and  are  attached  to 
the  main  framework.  It  will  be  seen  that  by  this  means  the 
tension  side  of  the  beam  is  on  top.  The  arrangement  for 
measuring  defections  is  fairly  obvious  from  the  illustration. 
J  is  a  light  wooden  cross  beam  supported  by  suitable  attach- 
ments from  either  end  fixed  on  the  neutral  axis  of  the  beam. 
By  means  of  the  levers  MN  and^Q  the  motion  of  M,  which  is 


204 


A  HANDBOOK  OF  TESTING  MATEEIALS 


attached  to  the  neutral  axis  of  the  beam,  is  magnified  on  a 
scale  P  attached  to  the  cross-beam  J.  The  loads  are  applied 
by  forcing  oil  into  the  cylinder  A  by  means  of  a  rotary  pump. 
Owing  to  there  being  no  packing,  and  consequently  very  slight 
friction,  loads  can  be  measured  by  observing  the  readings  of 
a  pressure-gauge  connected  to  the  cylinder. 

Such  an  arrangement  is  very  suitable  for  carrying  out  tests 
on  ferro- concrete  beams,  and  much  useful  research  has  been 
performed  on  a  machine  of  this  type  at  the  Manchester  School 


J                                         I 

II  r 

N 

(me     G 

M                                     1 

FIG.  124. — Amsler-Laffon  Beam  Testing  Machine. 

of  Technology,  under  the  direction  of  Mr.  W.  C.  Popplewell, 
M.Sc.1 

Ferro-Concrete  Floor  Tests. — In  rebuilding  the  town 
mansion  at  the  corner  of  Grosvenor  Square  and  North  Audley 
Street  the  architects,  Messrs.  Read  and  Macdonald,  of  Cork 
Street,  W.,  decided  to  construct  all  the  floors  of  ferro-concrete, 
partly  for  structural  reasons  and  partly  because  of  the  valuable 
fire-resisting  qualities  of  ferro-concrete.  On  April  10th,  1907, 
and  the  succeeding  five  days,  a  careful  series  of  load  tests  was 
made  by  Messrs.  Holloway  Bros.,  the  building  contractors, 
under  the  direction  of  the  architects.  The  area  selected  for 
the  purposes  of  the  tests  was  a  portion  of  the  first  floor, 

"  Proc.  lust.  Civ.  Eng.,"  vol.  clxxvii.,  pp.  3— IS. 


CEMENTS,   KEINFORCED   CONCRETE,   AND  STONES     205 


consisting  of  a  3-inch  slab,  measuring  19  feet  6  inches 
long  by  13  feet  3  inches  wide,  and  carried  by  two  beams 
projecting  6  inches  below  the  under  surface  of  the 
slab  by  8  inches  wide,  and  having  the  clear  span  of 
19  feet  6  inches  between  the  supports.  In  order  to  provide 
for  the  exact  registration  of  deflection,  three  instruments  were 
placed  beneath  one  of  the  beams  :  one  at  the  middle  of  the 

FLOOR  TESTS  AT  GROSVENOR  SQUARE. 


Date. 

Time. 

Load, 
Ibs.  per 
sq.  It. 

Deflection  in  Fractions  of  an  Inch. 

Left 
Hand. 

Right 
Hand. 

Centre. 

April  10,  1907 

0 

0 

0 

0 

5         5 

— 

100 

0-0355 

0-0355 

0-11 

5                      5 

— 

130 

0-055 

0-051 

0-15 

,                      , 

2.50p.m. 

159 

0-079 

0-083 

0-216 

>                      5 

3.10    „ 

159 

0-079 

0-083 

0-22 

5                       5 

3.25    ,, 

130 

0-071 

0-077 

0-193 

55                    5 

3.45    ,, 

100 

0-055 

0-063 

0-161 

11,                 , 

7.45  a.m. 

100 

0-063 

0-067 

0-165 

12, 

2.45  p.m. 

100 

0-067 

0-071 

0-173 

55        > 

3.0      „ 

72 

0-043 

0-055 

0-157 

55                  5 

3.15    „ 

42 

0-043 

0-047 

0-126 

55                   1                       • 

3.45    ,, 

13-5 

0-027 

0-037 

0-095 

55                  5 

4.15    „ 

0 

0-0161 

0-023 

0-063 

13,       , 

9.0    a.m. 

0 

0-0161 

0-012 

0-051 

14,       , 

12    noon 

0 

0-0161 

0-008 

0-043 

15,       , 

11.50a.m. 

0 

0-008 

o-ooo 

0-0431 

1  Instrument  has  probably  been  disturbed. 

span  and  the  other  two  at  the  distance  of  2  feet  9  inches  from 
the  supports.  Loading  was  effected  by  means  of  bricks  and 
Portland  cement  in  bags.  The  results  of  the  tests  are  sum- 
marised in  the  subjoined  table,  from  which  it  will  be  seen  that 
the  maximum  deflection  under  double  the  normal  superload  of 
84  Ibs.  per  sq.  foot  was  only  0*139  inch,  calculated  over  the 
central  14-foot  portion  of  the  beam,  or  j^to  °f  tne  span. 
No  records  were  taken  of  the  settlement  at  the  supporting 
walls,  so  it  would  not  be  fair  to  regard  the  maximum  deflection 
of  0'22  inch  as  having  taken  place  in  the  floor  itself.  But 


206 


A  HANDBOOK  OF  TESTING  MATERIALS 


adopting  that  value  for  the  sake  of  argument,  it  will  be  seen 
that  the  proportion  is  only  joVo  °f  the  entire  span,  or 
less  than  one-half  the  proportion  generally  allowed  by 
architects.  Another  point  worthy  of  special  note  is  that  on 
removal  of  the  loading  the  floor  returned  practically  to  its 
original  form,  thereby  demonstrating  the  perfect  elasticity  of 
the  construction. 

Stones,  Bricks,  etc. — These  materials  are  tested  in  com- 
pression in  a  similar  manner  to  that  described  for  cements. 
The  following  table  indicates  some  results  of  such  materials 
taken  from  Popplewell's  "  Testing  of  Materials  of  Construc- 
tion "  :— 

TABLE  XXVII. — CRUSHING  STRENGTH  OF  VARIOUS  STONES,  ETC. 


Material. 

Authority. 

Crushing  Strength. 

Tons  per  sq.  ft. 

Lbs.  per  sq.  in. 

Granite,  Aberdeen  Grey  . 

Unwin. 

1,412 

22,000 

„   .      Eed    . 

M 

1,614 

25,100 

Basalt,  Penmaenmawr      . 

Fail-bairn. 

1,086 

16,850 

Sandstone,  York  Grit 

Unwin. 

712 

11,050 

,,         Eed  Mansfield 

» 

609 

9,560 

Eed  Alton      .     _    . 

» 

309 

4,800 

Limestone,       White       Italian 

Marble  ..... 

Eennie. 

1,400 

21,800 

Limestone,  Portland    *    .         . 

Unwin: 

516 

8,020 

,,           Purbeck        .         . 

Eennie. 

587 

9,110 

,,           An  caster       .     '•:.. 

[      Eoyal 

150 

2,330 

(      Com. 

,,           Bramham  Moor     . 

y  > 

380 

5,900 

Bricks,  London  stock,  average 

Unwin. 

140 

2,180 

,,       Leicester,     wire     cut, 

average     . 

» 

290 

4,500 

,,       Staffordshire,  Common 

Blue  . 

" 

400 

6,210 

CHAPTEE  XI 

THE    TESTING    OF    TIMBER 

Tension  Tests.— Considerable  difficulty  is  encountered  in 
the  testing  of  timber  in  tension  owing  to  the  tendency  of  the 
material  to  crush  in  the  grips  or  to  shear.  The  portion  of  the 
specimen  which  enters  the  grips  should  be  large  in  proportion 
to  the  breaking  section,  and  should  be  extended  for  some 
distance  out  of  the  grips  before  being  gradually  reduced.  If 
it  is  difficult  to  develop  the  full  tensile  strength  of  timber  in  a 
testing  machine,  it  is  still  more  difficult  to  do  so  in  structures 
built  of  this  material ;  failure  invariably  taking  place  by 
shearing  or  splitting  at  both  connections.  For  this  reason 
tension  tests  in  timber  can  have  little  more  than  academic 
interest  except  in  a  few  isolated  cases.  Timber  is  furthermore 
extremely  variable  in  its  properties,  and,  like  all  other 
materials,  it  is  of  vital  importance  in  cases  of  important 
structures  that  strength  calculations  should  be  based  on  tests 
specially  carried  out  on  actual  samples  of  the  material 
employed.  The  amount  of  moisture,  for  instance,  will  greatly 
affect  the  results.  In  the  adjoining  tables,  however,  we  give 
some  standard  results  which  will  indicate  what  may  be 
expected  in  testing. 

Compression  Tests. — Unlike  metallic  materials,  the  full 
compressive  strength  is  frequently  developed  in  timber  struts, 
and  the  true  crushing  load  becomes  of  importance.  Tests  are 
generally  carried  out  on  cubes  or  short  cylinders,  which  should 
be  as  large  as  the  testing  machine  employed  will  conveniently 
take.  It  is  sometimes  useful  to  embe'd  the  ends  on  a  sheet  of 
millboard,  especially  if  the  ends  are  rough. 

Shear  and  Cross-bending  Tests. — Timber  is  in  the  majority 
of  cases  only  stressed  to  its  full  capacity  when  employed  as 


208  A  HANDBOOK  OF  TESTING  MATEEIALS 

beams,  and  hence  the  most  important  tests  are  those  in  which 
the  material  is  tested  in  the  same  manner.  "Whenever  possible 
full-size  beams  should  be  employed  and  tested  in  a  similar 
manner  to  iron  girders,  except  that  the  ordinary  knife-edges 
should  be  prevented  from  penetrating  the  fibres  by  placing 
a  piece  of  iron  plate  between  the  knife-edge  and  the 
wood. 

If  the  depth  is  at  all  great  compared  with  the  length, 
failure  will  invariably  take  place  by  shear  along  the  length  of 
the  beam,  and  hence  the  shear  strength  becomes  of  consider- 
able importance.  Shear  strength  can  be  deduced  either  from 
beam  tests  carried  out  so  as  to  cause  the  material  to  fail  in 
this  manner,  or  by  direct  experiment.  In  all  practical  struc- 
tures shear  failure  will  take  place  along  the  fibres,  the  strength 
across  the  grain  being  much  more  than  along  the  grain. 

With  a  beam  supported  at  the  ends  and  loaded  centrally, 
the  maximum  bending  moment  is 

WL 
4"' 

"  W  "  being  the  central  load  and  "  L  "  the  span. 

But  bending  moment  M  =  SZ,  where  S  =  stress  in  the 
outermost  fibres,  and  Z  =  modulus  of  the  section. 

With  wood,  however,  it  is  usual  to  introduce  a  constant  into 
this  equation  : 

.  •  .  M=KSZ, 

WL 
but  M:=-—  , 


bd? 
And  "  Z  "  for  a  rectangular  beam—— 

where  1=  width  of  beam, 

and  d=  depth  of  beam. 

WL 


For  samples  of  the  same  wood  "  S  "  should  be  approximately 
constant. 


THE  TESTING  OF  TIMBEE 
Then  uniting  all  the  constants 


209 


Then  K=WL 
bd*' 

This  expression  should  remain  fairly  constant  for  samples 
of  the  same  wood,  and  consequently  is  often  used  com- 
mercially as  a  standard  of  comparison. 


TABLE  XXVIII.— TESTS  OF  TIMBER  IN  TENSION  AND  COMPRESSION,  BY 
MR.  T.  LASLETT. 

Carried  out  on  tension  specimens  2  inches  square,  30  inches  long,  and 
compression  specimens  about  1,  2,  3  and  4  inch  cube;  crushed  in 
direction  of  fibre. 


Kind  of  Timber. 

Sp.  Grav. 

Ult.  Resist,  in 
Ibs.  per  sq.  in. 
(Tension.) 

Ult.  Resist,  in 
Ibs.  per  sq.  in. 
(Compression.) 

English  Oak  (unseasoned) 

0-858 

3,837 

4,900 

,,          ,,    (seasoned)   .        . 

0-893 

7,571 

7,480 

French  Oak     .         .         .         . 

0-976 

8,102 

7,950 

Dantzic  Oak    .         .         .         . 

0-838 

4,217 

7,480 

American  White  Oak 

0-969 

7,021 

6,070 

American  Oak  (Baltimore) 

0-762 

3,832 

5,890 

African  Oak  (Teak) 

0-971 

7,052 

— 

Teak,  Moulmein      .         ,         . 

0-777 

3,301 

5,730 

Iron  Wood,  Burmah 

1-176 

9,656 

11,670 

Chow,  Borneo  .... 

1-134 

7,199 

12,590 

Greenheart,  Guian  .    '     . 

1-141 

8,820 

14,420 

Sabien,  Cuba   .         .    '  •    ;•       . 

0-917 

5,558 

8,470 

Mahogany,  Spanish 
,,          Honduras 

0-765 
0-659 

3,791 
2,998 

6,400 
6,380 

,,          Mexican 

0-655 

3,427 

5,600 

Eucalyptus,  Australian   . 

— 

— 

— 

Tewart     .         .    T..       .         ."- 

1-169 

10,284 

9,350 

Mahogany        .  ;     >  ".       • 

0-996 

2,940 

7,170 

Iron-bark         ,-'•,".         . 

1-150 

8,377 

10,300 

Blue  Gum        .... 

1-049 

6,048 

6,900 

Ash,  English   .... 

0-750 

3,780 

6,970 

Ash,  Canadian 

0-588 

5,495 

5,490 

Beech       ..... 

0-705 

4,853 

— 

Elm,  English  .... 

0-642 

5,460 

5,780 

Eock  Elm,  Canadian 

0-748 

9,182 

8,580 

T.M. 


210 


A  HANDBOOK  OF  TESTING  MATEEIALS 


TABLE  XXVIII. -Continued. 


Kind  of  Timber. 

Sp.  Grav. 

Ult.  Resist,  in 
Ibs.  per  sq.  in. 
(Tension.) 

Ult.  Resist,  in. 
Ibs.  per  sq.  in. 
(Compression.) 

Hornbeam,  England 

0-819 

6,405 

8,310 

Fir,  Dantzic     .        .        .         . 

0-603 

3,231 

6,940 

,,    Eiga          .... 

0-553 

4,051 

5,240 

„    Spruce,  Canadian 

0-484 

3,934 

4,850 

Larch,  Kussia  .        . 

0-649 

4,203 

5,820 

Cedar,  Cuba     .... 

0-469 

2,870 

4,480 

Red  Pine,  Canada    .        .    •    . 

0-553 

2,705 

5,690 

Yellow  Pine,  Canada 

0-551 

2,759 

4,210 

Pitch  Pine,  American 

0-659 

4,666 

6,470 

Kauri  Pipe,  New  Zealand 

0-544 

4,040 

6,430 

Hatfield's  experiments.* 


Georgia  Pine,  American  . 
Locust,  American    . 
White  Oak,  American 
Spruce,  American     . 
White  Pine,  American     . 
Hemlock  .         ... 

— 

16,000 
24,800 
19,500 
19,500 
12,000 
8,700 

\ 

*  These  experiments  were  carried  out  on  specimens  only  0'35  inch  round, 
such  a  size  being  far  too  small. 


TABLE  XXIX.— LAWSA'S  TESTS  OF  AMERICAN  TIMBERS,  12  FEET  AND 
2  FEET  LONG;  FAILURE  BY  DIRECT  CRUSHING. 


Name  of  Timber. 

Sectional  Area  in 
sq.  in. 

Ult.  Strength  in 
Ibs.  per  sq.  in. 

Coeff.  of  Elasticity, 
Ibs.  per  sq.  in. 

Yellow  Pine  . 

42  to  102 

4,544 

1,996,351 

White  Oak     . 

32  to  93 

3,470 

1,398,908 

Old  and  seasoned  White 
Oak    . 

28  to  87 

3,957 

1,817,539 

THE  TESTING  OF  TIMBER 


211 


TABLE  XXX. — KIRKALDY'S  EXPERIMENTS  ON  BEAMS. 


Description  of 
Timber. 

Breadth  and  Depth 
in  inches. 

Span  in  feet. 

Modulus 
of 
Rupture 
in  Ibs. 
per 
sq.  in. 

Modulus  of 
Elasticity, 
Ibs.  per  sq.  in. 

Pitch  Pine 

(  from  IMSX  11-30 
(     to    13-10X13-10 

12 

7,626 



Daiitzic  Eir 

(from  10-00x12-00 
(     to    13-25x14-38 

from  8  to  12 

4,581 

— 

»          >i 

(from    2-50x10-10 
!     to      3-00  X  10-10  j 

10 

3,726 

571,760 

Baltic  Oak. 

6-4x16-00 

10 

7,686 



Baltic  Eed  . 

(from  11-72x11-82 
(     to    11-77x11-86) 

12 

4,890 

— 

English  Oak 

(from    4-55x12-00) 
(     to      4-58X12-00 

10 

9,762 

— 

St.  Petersburg    . 

(        3-09x11-07 
(        3-08X11-02 

13 

8,187 

2,446,000 

St.      Petersburg 
1st  Yellow      . 

(from    2-75  X   8'7o 
(     to      3-00  X  8-75 

10 

8,556 

1,677,500 

St.      Petersburg 
2nd  Yellow     . 

(  from    2-87  X   8'75  \ 
to      2-99  X    8-75 

10 

6,918 

1,396,700 

Archangel  . 

(from    3-00x11-06 
(     to      3-09x11-02 

13 

6,738 

2,014,300 

Archangel    Deal 

2A  . 

3-00x3-00 

10 

6,252 

2,043,000 

Swedish 

(from    3-08X11-07 
(     to      4-10X    9-10 

10  to  13 

5,663 

1,838,300 

Swedish  SS 

(  from    3-00  X   9'10 
(     to      3-15  X   9-10 

10 

6,258 

1,149,600 

Swedish  DDD    . 

(from    2-93  X   8'75 
1     to      2-95  X   8-75) 

10 

6,978 

1,528,700 

The  Modulus  of  Elasticity  is  generally  deduced  from  beam 
tests,  but  in  employing  figures  thus  obtained  it  should  be 
remembered  that  time  has  considerable  effect  on  the  elastic 
properties  of  timber,  and  tests  extended  over  long  periods  have 
shown  that,  roughly  speaking,  the  permanent  deflection 
attained  after  six  months  or  more  may  be  taken  as  at  least 
twice  the  value  obtained  on  tests  of  short  duration. 

Tables  XXIX.  and  XXX.,  taken  from  different  sources, 
give  results  obtained  by  the  above  methods. 

p  2 


212  A  HANDBOOK  OF  TESTING  MATEEIALS 

TABLE  XXXI.— SHE AR  STRENGTH  OF  TIMBER. 


Kind  of  Timber. 

Shearing  Strength,  Ibs.  per  sq.  in. 

Authority. 

Maximum. 

Minimum. 

Ash        . 

700 

458 

Watertown  Arsenal 

Yellow  Birch 

, 

815 

563 

tests 

White  Maple 

647 

367 

EedOak 

. 

999 

726 

White  Oak     . 

966 

752 

White  Pine    . 

366 

267 

Yellow  Pine  . 

415 

286 

Spruce   .         . 

, 

374 

253 

Whitewood    . 

406 

382 

Eed  Fir  A      . 

, 

517 

146 

Ha 

tt.* 

„     „   B      . 

273 

173 

„      „   0      . 

395 

74 

Longleaf  Pine  (Georgia) 

291 

247 

*  These  results  were  obtained  as  the  resistance  to  splitting  due  to  longitudinal 
shear  under  cross  bending. 

Ligno- Concrete. — The  author  has  recently  made  some  rough 
tests1  on  concrete  reinforced  with  wood.  Interesting  results 
will  be  obtained  if  hard  and  soft  woods  are  used.  Com- 
parisons may  also  be  made  with  concrete  reinforced  with 
steel.  Further  tests  may  be  devised  by  varying  the  shape  of 
a  wooden  framework  round  which  is  placed  the  concrete. 


Enginyering,  1910. 


CHAPTEE  XII 

EXPERIMENTS    IN    COLLEGE    LABORATORIES 

ONE  of  the  regular  parts  of  every  engineering  student's 
course  of  study  is  the  carrying  out  of  tests  in  a  materials 
testing  laboratory,  and  the  following  is  suggested  as  a  suitable 
and  systematic  series  of  experiments.  It  is  assumed  that  the 
student  has  already  completed  a  first-year's  course  in  applied 
mechanics,  and  is  familiar  with  the  use  of  verniers,  micro- 
meters, microscopes,  etc.  Few  students  will  have  the 
opportunity  to  carry  out  all  of  the  tests  mentioned,  and  much 
must,  of  course,  depend  on  the  resources  of  the  particular 
laboratory  in  which  the  student  is  working.  It  is  not  even 
suggested  that  the  experiments  should  be  carried  out  strictly 
in  the  order  given,  although  an  attempt  has  been  made  to 
arrange  them  as  far  as  possible  in  the  usual  order  in  which 
they  should  be  performed.  The  general  instructions  to  the 
student  should  be  carefully  read  and,  subject  to  the  dis- 
cretion of  the  particular  professor  under  whom  the  student  is 
working,  adhered  to  faithfully.  It  is  hoped  that  the  tables 
prepared  for  "  setting  "  these  experiments  will  be  found  useful 
by  both  students  and  demonstrators.  They  are  intended  to 
show  at  a  glance  the  work  which  has  already  been  done 
by  the  student,  and  suggesting  fresh  experiments  to  be 
performed. 

GENERAL   INSTRUCTIONS   TO    STUDENT. 

Note-Books. — Each  student  should  be  provided  with  a 
note-book  for  entering  records  of  all  laboratory  tests  and 
illustrative  sketches.  In  any  case  this  book  should  have  good 
paper  and  be  provided  with  stiff  binding.  The  following 
method  has  been  found  excellent  for  students  preparing  for  a 
degree  in  engineering. 


214  A  HANDBOOK  OF  TESTING  MATERIALS 

All  notes  and  descriptions  should  be  on  separate  sheets  of 
thick  foolscap ;  curves  on  foolscap  size  sheets  of  squared 
paper ;  diagrams  on  drawing  paper  and  photographs  pasted 
on  same.  All  these  can  be  bound  up  at  the  end  of  the  session 
at  quite  a  small  cost.  Needless  to  say,  blank  pages  should  be 
left  for  further  .additions.  Such  a  book,  even  apart  from 
examinations,  is  an  excellent  record  of  a  student's  work  and 
neatness,  suitable  for  showing  to  a  prospective  employer.  In 
all  cases  a  good  wide  margin  should  be  left  at  the  side  of  the 
page ;  when  separate  sheets  are  used  an  allowance  for  binding 
is  necessary.  On  no  account  should  different  subjects  (such 
as  heat  engines  and  materials)  be  mixed  in  the  same  note- 
book. 

Before  starting  an  experiment  the  student  should  make  a 
sketch  of  the  apparatus  to  be  used,  employing  diagrammatic 
sketches  rather  than  scale  drawings.  He  should  then  calculate 
approximate  data  so  as  to  know  what  to  expect  during  the 
experiment.  Thus  in  the  case  of  the  determination  of  Young's 
modulus  he  should  measure  the  specimen,  and  look  up  in  the 
tables  the  stress  at  the  elastic  limit  of  the  material.  He  will 
then  be  able  to  form  an  estimate  of  the  load  which  the 
specimen  can  safely  withstand  without  damaging  the  instru- 
ment. This  must  be  well  within  the  calculated  elastic  limit  of 
the  material. 

In  marking  out  specimens  centrepops  should  be  light,  as 
in  testing  to  destruction  it  is  possible  that  they  may  have  a 
considerable  effect  on  the  ultimate  strength. 

The  greatest  care  should  be  taken  with  instruments  and 
apparatus  of  all  kinds.  Instruments,  of  precision,  such  as 
extensometers,  cannot  be  handled  too  carefully. 

Before  testing  the  student  should  enter  in  his  rough  book 
the  date,  and  as  far  as  possible  every  dimension  which  can 
possibly  affect  the  result.  Nothing  is  more  annoying  than  to 
find,  after  a  long  and  careful  experiment  lasting  over,  perhaps, 
two  or  three  days,  that  some  vital  dimension  was  not  taken  at 
the  beginning,  and  as  a  consequence  the  whole  test  spoiled. 
During  the  test  every  reading  should  be  entered  in  the  rough 


EXPERIMENTS  IN  COLLEGE  LABOEATORIES          215 

book  directly  it  has  been  taken  ;  never  trust  the  memory  more 
than  a  few  minutes  when  carrying  out  scientific  work. 

.  As  soon  after  the  finish  of  the  test  as  is  possible  a  full  report 
of  the  experiment  and  apparatus  used  should  be  written  up  in 
the  recording  note-book  stating:  (a)  object  of  test;  (b)  apparatus 
employed,  including  details,  with  sketches,  if  necessary,  of 
such  parts  as  grips,  shape  of  specimen,  etc. ;  (c)  order  of 
making  observations ;  (d)  record  of  observations  ;  (e)  deduced 
results  showing  carefully  how  such  were  obtained;  (/)  graphical 
representation  of  results  when  possible  ;  (g)  comparison  with 
standard  laws  or  results  to  be  verified. 

Wherever  possible,  photographs  of  apparatus,  specimens, 
fractures,  etc.,  should  be  pasted  into  the  note-book. 

In  describing  experiments  it  cannot  be  too  strongly  impressed 
that  language  is  "  the  first  tool  of  the  mind."  Great  care 
should  be  taken  by  the  student  in  expressing  clearly  and  in 
suitable  words  any  work  upon  which  he  has  to  write  a  report. 
Inaccuracy  of  expression  is  as  great  a  source  of  error  as 
inaccuracy  of  observation.  Huxley's  theory  of  style  was  "  to 
say  that  which  has  to  be  said  in  such  language  that  you  can 
stand  cross-examination  on  each  word." 

EXPERIMENTS    SUITABLE   FOE  COLLEGE  LABORATORIES. 
On    Wires    and   Springs. 

1.  To  Determine  the  Relation  between  Load  and  Extension 
of  a  Spring. — The  apparatus  is   usually  found  set  up,  and 
consists  simply  of  a  spring  attached  to  a  hook  at  the  top  and 
provided   with   a   scale   pan   or   similar   contrivance   at   the 
bottom.     A  vernier  moving  over  a  scale  gives  the  deflection. 
Load  with  increasing  weights  so  as  to  get  ten  or  more  readings, 
and  plot  a  curve  showing  the  above  relation.  It  should  come  out 
a  perfectly  straight  line.  Deduce  the  "  slope  "  of  same  and  note. 

2.  To  Determine  Relation  between  Load  and  Compression 
of  a  Spring. — This  is  carried  out  in  an  exactly  similar  manner 
to  experiment  1,  and  similar  results  deduced. 

3.  Extension   of  a    Short    Wire    to   Determine  Young's 
Modulus. — See  page  165  for  general  description.     Care  should 


216  A  HANDBOOK  OF  TESTING  MATEEIALS 

be  taken  not  to  overload  the  wire.  Take  as  many  readings  as 
possible,  plot  curve  as  in  experiment  1,  deduce  Young's 
modulus  from  slope  of  curve  and  the  dimensions  of  the  wire. 
This  experiment  may  be  repeated  for  wires  of  different  material. 

4.  Extension    of    a    Long   Wire. — Some   laboratories   are 
provided    with   a   very    long    wire    (say   90    feet   or   more) 
running  on  pulleys  down  the  laboratory.     Readings   as   in 
experiment    3,   but    only    scale    and    vernier   necessary   for 
extension.     Take  readings  with  increasing  load  and  decreasing 
load ;  plot  curves  for  both  sets  of  readings.      The  curves  will 
not  coincide  owing  to  friction  of   pulleys,  hence  take  mean 
of  the  two  sets  and  deduce  value  of  as  before. 

5.  Wire  Stressed  to  Fracture  on  Autographic  Apparatus. — 
(See  description  of  this  experiment  on  p.  166.)     It  is  not 
desirable  to  ink  in  autographic  diagrams  if  they  are  drawn  by 
a  pencil  apparatus,  but,  if  faint,  it  is  allowable  to  dot  with  a 
sharp  pencil  or  a  pen  along  the  line  traced  out.     Copies  may 
be  taken  with  tracing  paper. 

6.1  Value  of  C  by  Torsional  Deflection  of  a  Wire. — (See 
p.  135.)  Take  increasing  and  decreasing  loads  as  before  and 
obtain  mean  value  to  eliminate  friction.  Value  of  C  deduced 

from  the  formula 

n_584  Ml 
0D4     ' 

where  M  is  twisting  moment  in  Ibs.  inches,  /  the  length 
in  inches,  D  the  diameter  of  wire  in  inches,  and  6  the  twist  in 

M 

degrees.     Obtain  the  mean  value  of  -^  by  plotting  a  curve 

showing  relation  between  them.  This  should  come  out  to  a 
straight  line. 

7.1  Value  of  C  by  Torsional  Vibrations  of  a  Wire.— (See 
p.  136.) 

Value  of  C  deduced  from  0=^ 

gd*  \_    t 

where  mi,  ???2,  #,  etc.,  have  the  values  given  on  p.  136. 


1  If  same  kind  of  wire  is  employed  for  experiments  3,  6,  and  7,  the  value  of 
oisson's  ratio 
Poisson's  ratio. 


Poisson's  ratio  should  be  deduced  from  formula   E  =  - "       '  where    -   is 

n  n 


EXPEEIMENTS  IN  COLLEGE  LABOKATOKIES          217 

8.  Spring  Tested  in  Extension  for  Value  of  C,  and 

9.  Spring  Tested  in  Compression  for  Yalue  of  C. — These 
experiments  can  be  carried  out  in  a  similar  manner  to  experi- 
ments 1  and  2,  but  for  large  springs  either  a  special  apparatus 
is  employed,  or  in  the  case  of  9  this  can  be  performed  in  an 
ordinary  testing  machine  arranged  for  compression.     Deflec- 
tion can  be  taken  in  the  latter  case  by  measuring  with  an 
internal  micrometer  between  the  compression  plates. 

.    ~     2-55  D2LW 
C  is  obtained  from  the  formula  C= — -^ , 

O    Ci 

where   D    is   mean   diameter   of    coils,   L     total   length    of 
spring    if   pulled   out  to  a  plain   rod   (approx.    nirD),    d    is 

W 

diameter  of  wire,  and  -r-  relation  between  load  and  deflection 
o 

— obtained  by  plotting  a  curve. 

EXPERIMENTS  WITH  TESTING  MACHINES  (TENSION). 

10.  Testing  Small  Specimen  for  Yield  Point  and  Fracture 
in   a  Small  Testing  Machine. — Some   such  machine  as  the 
Bailey   machine   can  be  employed  (see  p.  121).      As  many 
materials   as   the  student  has  time  and  opportunity  to  test 
should  be  employed;  in  any  case  (a),1  (c),  and  (e). 

11.  Calculating     Mechanical    Advantage     of    a    Large 
Testing    Machine     and     Checking    for    Sensitiveness    and 
Accuracy. — See  p.  47  for  such  a  test  fully  worked  out. 

12.  Yield  Point  of  Full  Size  Specimen  by  drop  of  beam. 
This  will  also  give   experience  in  working   a   machine  and 
setting  up  specimens  (see  p.  85).     Materials  suggested,  (a), 
(b),  (e),  and  (g). 

13.  Fracture    of   Various   Materials. — This   involves   the 
marking  out  of  specimens,  setting  up,  determination  of  yield 
point  and  measurement  of  elongation  per  cent.,  reduction  of 
area,  etc.    (see   pp.    86,  87,  and    89).     Materials   suggested, 
(a),  (b),  (c),  (d),  (e),  (/),  (0),and(fc). 

14.  Full    Commercial    Test. — Test,    say,     half    a    dozen 

1  These   letters   refer  to  mild    steel  («),   wrought  iron  (J),  cast  iron  (c), 
copper  (d),  brass  (e),  gun  metal  (/),  aluminium  (rolled)  (#),  tool  steel  (/<?). 


218  A   HANDBOOK  OF  TESTING  MATERIALS 

specimens  of  the  same  material  as  in  experiment  13,  carefully 
noting  kind  of  fracture,  etc. ;  compare  with  a  standard 
specification  (see  Appendix  II.),  draw  up  a  full  report  on  the 
material  (see  pp.  5  and  85). 

15.  Test  to  Fracture  with  Autographic    Diagram. — This 
will   depend   on   the   machine  at  disposal  of  student.      See 
pp.   72   to   82   for   description    of    various    methods.      The 
yield  point,  maximum   load,  and  breaking   load   should   as 
far   as    possible   be   read   independent    of    the    autographic 
apparatus  and  noted.     Mark  all  particulars  of    test  on  the 
autographic  diagram  itself,  together  with  yield  stress,  etc. 

16.  Determination  of  Young's  Modulus  with  medium  and 
full-size  specimens.     See  Chap.  IV.  for  various  types  of  strain- 
measuring  instruments.     Preliminary  experiments  should  be 
made  on  a  small  machine  such  as  that  made  by  the  Cambridge 
Scientific  Instrument  Making  Company.    Great  care  should 
be  taken  in  testing  cast  materials  that  the  breaking  load  is  not 
approached,  as  the  fracture  of  the  specimen  with  some  types 
of  extensometer  is  disastrous. 

17.  Determination  of  Elastic  Limit   by  Extensometer.— 
Increase  the  load  by  small  and  uniform  amounts,  calculating 
after  each  reading  the  increase  in  length.     The  passing  of  the 
elastic  limit  will  be  observed  by  an  increase  in  the  extension 
per  unit  load.    Materials  suggested,  (a),  (b),  (d),  and  (g).   If  (a) 
is  a  good  specimen,  the  elastic  limit  will  practically  coincide 
with  the  yield  point. 

18.  Time  Effect  on  Hardening. — Fit  specimen  with  extenso- 
meter, take  load  up  just  beyond  first  appearance  of  yield,  and 
keep    load    constant     until    no    further  slipping.      Slightly 
increase  load,  and  note  time  and  extension  until  slipping  again 
ceases.      Repeat  with  further  loads  until  complete  breakdown. 
Plot  stress-strain  curve  and  mark  on  times.     See  p.  104. 

19.  Artificial  Raising  of  Elastic  Limit  by  Overstraining. 
— Take  extensions  up  to  beyond  yield  point,  remove  load  and 
repeat  taking  load  somewhat  higher  than  previously.     Eepeat 
this  several  times  until  complete  breakdown,  and  plot  series  of 
curves  so  as  to  show  comparison.     See  p.  102,  etc. 


EXPERIMENTS  IN  COLLEGE  LABORATORIES          219 

20.  Effect  of  Boiling  Water  on  Overstrain. — Eepeat  experi- 
ment 19,  but  after  each  loading  boil  specimen  at  100°  C.  for 
ten  minutes.     Plot  curves  as  before.     Try  also  allowing  the 
specimen  to  stand  for  one  or  more  days.     See  p.  104. 

21.  Annealing  Tests. — Kun  a  series  of  tests  on  specimens 
of  (a),  (d),  and  (ft),  trying  the  effect  of  annealing  in  an  oven 
at  various  temperatures.     See  pp.  104  and  Appendix  IV. 

22.  Effect  of  Notches. — Eun  a  series  of  breakdown  tests  on 
specimens  which  have  been  slightly  notched  with  a  triangular 
file  to  varying  depths.     Try  also  effect  of  sudden  changes  of 
cross-section  by  machining   pieces   out  of  the   sides   of  flat 
specimens. 

COMPEESSION  TESTS. 

23.  Compression    of    Short    Specimens  (ductile). —  Short 
specimens  can  be  tested  for  yield  point  (when  this  is  well 
marked),  and  complete  breakdown  as  with  tension  tests.      See 
p.  89. 

24.  Compression  of  Short  Specimens  (brittle). — Cast  iron 
is  the  usual  material  employed.     Care  should  be  taken  that, 
when  fracture  takes  place,  the  broken  pieces  cannot  fly  out 
and  injure  anybody.     It  is  a  good  practice  to  place  a  piece  of 
sacking  so  as  to  prevent  this  kind  of  accident.     See  p.  93. 

25.  Effecting    of    Bedding.— Eepeat   23    and    24,    using 
pieces   of    soft   lead   or   copper  between    the  specimen   and 
compression  plates,  and  compare  results. 

26.  Testing  of  Struts.— (See  p.  47.)     (a)  Free  ends.     Eun 
a     series    with    varying     length     and     constant    diameter, 
using   a    ball   so   as    to   secure    that   ends   are   quite    free. 
Plot   relation   between   buckling   load  and    length,  and    try 
checking   Gordon's   or  Eankine's  formulae,      (b)  Fixed  ends. 
Take  two  cast-iron   blocks  in  which  a  hole  has  been  drilled 
the   same  diameter  as  the  specimen.     Cut  off  a  number  of 
lengths  from  a  mild-steel  bar  and  drive  into  the  blocks.    Plot 
as  in  (a)  ;    f"  is  a  suitable  diameter  for    both  (a)  and  (b). 
(c)  Hollow  struts.     Eun  a  series  of  tests  with  drawn  tubes. 
Mild  steel  or  brass  are  suitable  materials. 


220  A  HANDBOOK  OF  TESTING  MATEEIALS 

27.  Alternate   Tension    and   Compression.— Try  some  of 
the  experiments  18,  19,  20,  and  21  in  alternate  tension  and 
compression.     Find  if  there  is  an  elastic  range,  i.e.,  whether 
raising  the  yield  point  in  tension  lowers  it  in  compression. 

BENDING  TESTS. 

28.  Testing  of  Beams  (deflection). — These  can  be  carried 
out  on  the  machine  described  on  p.  39,  or  on  a  universal 
testing  machine  set  up  for  beam  testing.     As  far  as  possible 
test  beams  and  cantilevers  in  deflection  with  various  methods 
of  fixing,  supported  at  both  ends,  fixed  at  both  ends,  etc.,  and 
compare  results  with  the  standard  formula.     Obtain  Young's 
modulus. 

29.  Breaking  of  Beams. — Test  various  lengths  of  cast-iron 
beams  for  fracture.     Where  facilities  are  provided,  full-size 
girders,  both  plain  and  built  up,  can  be  tested  in  the  same 
manner. 

30.  Obtaining  Elastic  Curve. — This  is  carried  out  on  an 
apparatus    similar   to   that   described   on   p.    41.      Compare 
results  with  those  obtained  by  formula. 

TORSION  TESTS. 

81.  Obtaining  C. — Some  such  machine  as  is  described 
on  p.  119  can  be  employed,  using  a  torsional  deflectometer  as 
on  p.  154.  The  value  of  C  is  calculated  as  in  experiment  6. 

32.  Fracture  of  Torsion  Specimens. — This  can  be  carried 
out  either  on  a   special  machine  or  on  a  universal  testing 
machine  provided  with  torsion  attachment.     See  pp.  119  and 
121.     Specimens   both  solid  and  hollow  should    be    tested. 
When  possible,  observe  whether  any  change  takes  place  in 
length  of  specimen. 

33.  Effect    of    Flaws  and    Surface    Markings. —Try   the 
effect  of  slightly  cutting  notches  with  a  lathe  tool  into  the 
surface  of  a  torsional  specimen. 

MISCELLANEOUS  TESTS. 

34.  Impact  Tests  on  Plain  and  Notched  Specimens. — See 

pp.  137  to  149  for  various  machines  and  methods. 


EXPEEIMENTS  IN  COLLEGE  LABORATOEIES          221 

35.  Shear  Tests,  double  and  single. — See  p.  155  for  descrip- 
tion of  shear  shackles,  etc.,  and  method  employed. 

36.  Punching  Tests.— See  p.  159. 

37.  Cold    Bending   Tests. — Try    several    specimens,    and 
compare  with  specification  on  p.  '234. 

38.  Hammering  Tests. — Test  samples  as  forged,  cold-drawn 
and  annealed  specimens  of  copper,  and  compare  with  clauses  1 
and  2,  Appendix  II.,  p.  234. 

39.  Rough  Examination  of  Microstructure. — See  p.  9. 
.40.  Repeat  Stresses. — This  requires  special  apparatus,  and 

depends  on  the  facilities  of  the  laboratory.  Sankey's  band- 
bending  machine  (see  p.  181)  is  a  useful  instrument  for  a 
laboratory  not  otherwise  provided. 

41.  Combined    Bending    and    Torsion. — Many   instructive 
experiments  can  be  carried  out  in  this  direction  by  methods 
which  will  readily  suggest  themselves.     Eesults  on  cast-iron 
test  pieces  are  given  on  p.  251. 

42.  Combined  Torsion   and  Direct  Stresses. — See  p.  236 
and  Bibliography.     Much  research  work  still  remains  to  be 
done  on  this  subject.      Original  papers  of   previous    experi- 
menters should  be  consulted  before  fresh  work  is  started. 

43.  Tests   of  Balls. — A  series   of  experiments   should   be 
carried  out  on  increasing  sizes  of  balls  (either  cast  steel  or  gun 
metal),  according   to   some  such  method  as  is  described  on 
p.  161.      Curves  should  be  drawn  showing  relation  between 
fracture  load  and  diameter. 

44.  Hardness  Tests. — These  can  be  performed  by  any  of  the 
methods  described  on  pp.  145  to  154.     Whichever  method  is 
employed,  it  is  advisable  to  run  a  comparative  test  on  such 
standard    materials  as    soft    annealed   Swedish  iron  or   soft 
annealed  electrolytic   pure   copper.      Hardness   can  only  be 
expressed   by  comparison,  and   consequently  this  should  be 
clearly  brought  out  in  the  results. 

45.  Find  Relation  Between  Hardness  Number  and  Tensile 
Strength. — Use   range   of  materials   closely  allied,    such    as 
steels  with  varying  percentage  of  carbon,  and  see  if  a  constant 
law  can  be  obtained.     See  p.  151. 


222  A  HANDBOOK  OF  TESTING  MATERIALS 

46.  Testing  Thick  Cylinder.— Test  a  brittle  material.     The 
specimen   to    be   turned   inside  and  out  and  fitted  with  an 
accurately  turned  plunger ;  partially  fill  the  inside  hole  with 
paraffin  wax,  and  load  with  compression  machine. 

TESTING  OF  TIMBER. 

Consult  Chapter  V.  for  various  methods  and  probable  results. 

47.  Timber    Tests   in    Tension. — Carry    out     by   method 
described  on  p.  207,  using  as  many  specimens  and  as  many 
different  varieties  of  timber  as  possible. 

48.  Crushing  Timber.— See  p.  207. 

49.  Shearing  Tests  on  Short  Beams.— See  p.  208. 

50.  Testing  of  Long  Timber  Beams.— Test  for  deflection, 
and,  as  far  as  possible,  look  for  increase  of  deflection  with 
time. 

51.  Testing  Long  Timber  Struts. — Eun  a  series  of  varying 
lengths,  and  check  with  standard  formula. 


TESTING  OF  CEMENTS  AND  CONCRETE. 

Consult  Chapter  V.,  and,  as  far  as  possible,  adhere  to  the 
methods  suggested  there.  The  following  tests  will  be  found 
described  on  pp.  189  to  204. 

52.  Specific  Gravity  Test. — Special  specific  gravity  bottles 
are  made  for  this  work,  but  ordinary  apparatus  and  methods 
can,  of  course,  be  employed.     Use  petroleum  as  displacement 
liquid. 

53.  Setting  Test.— Try  various  cements  and  different  pro- 
portions in  concrete,  also  try  varying  percentage  of  water. 

54.  Tensile  Tests. — Prepare  standard  briquettes  according 
to   method   described  on   p.  190,   and   compare  results  with 
minimum  specification. 

55.  CompressiYe  Tests.— See  p.  194. 

56.  Soundness  Test.— Use  the   Le  Chatellier  method,  as 
described  on  p.  192. 

57.  Compressive  Tests  on  Stones.— See  pp.  194  and  206. 


EXPEEIMENTS  IN  COLLEGE  LABOEATOEIES          223 


TABLE  XXXII. — RECORD  OF  LABORATORY  EXPERIMENTS, 

Experiments  carried  out  by_ 


Experi- 
ment No. 

Description  of  Experiment. 

Set  by. 

Date. 

Examined 

by. 

Date. 

1 

Relation  between  load  and  ex- 
tension of  spring  . 

2 

Relation  between  load  and  com- 

pression        .... 

3 

Determination  of  E   on  short 

wire       

4 

Determination   of    E   on  long 
wire      

5 

Test  of    wire  on   autographic 
apparatus      .... 

6 

Value  of  C  by  torsional  deflec- 
tion of  wire  .... 

7 

Value  of  0  by  oscillation  method 

8 

„       ,,   by  spring  in  tension 

9 

,,       ,,   in  compression 

10 

Determination   of   yield  point 
on  small  machine  . 

11 

Checking     of     large      testing 
machine        .... 

12 

Yield  point  011  large  machine  . 

13 

Eracture  of  various  materials  . 

14 

Complete  commercial  test  and 
report    

15 

Test    to    fracture    with   auto- 
graphic diagram    . 

224  A  HANDBOOK  OF  TESTING  MATERIALS 

TABLE  XXXII.— Continued. 


Experi- 
ment No. 

Description  of  Experiment. 

Set  by. 

Date. 

Examined 

by. 

Date. 

16 

Determination      of       Young's 
modulus  with  exteusometer 

17 

Elastic  limit  by  extensometer  . 

18 

Hardening  effect  of  time,  etc.  . 

* 

19 

Artificial    raising     of     elastic 
limit       .         .         .                  . 

• 

20 

Effect     of     low     temperature 
annealing      .... 

21 

Effect    of    nigh    temperature 
annealing      .         .        .        , 

22 

Effect     of     notching     tension 
specimen       .         .         . 

23 

Ductile     specimens    in    com- 
pression        .         . 

24 

Brittle     specimens     in     com- 
pression       .         ... 

2o 

Effect  of  bedding  specimens     . 

• 

26 

Tests  on  struts,  (a),  (Z>),  and  (c) 

27 

Alternate    tension    and    com- 

pression       .         . 

28 

Deflection  of  beams. 

29 

Breaking  of  beams  . 

30 

Elastic  curve  of  beams     . 

31 

Determination    of    C    (torsion 
test)      ... 

EXPERIMENTS  IN  COLLEGE  LABORATORIES          225 


TABLE  XXXII.— Continued. 


Experi- 
ment No. 

Description  of  Experiment. 

Set  by. 

Date. 

Examined 

by. 

Date. 

32 

Fracture  of  torsion  specimen   . 

33 

Effect    of    flaws    and    surface 
markings  (torsion) 

34 

Impact  tests     .         . 

35 

Shear  tests        .         .        . 

36 

Punching  tests         .         .         . 

37 

Cold  bending  tests   . 

38 

Hammering  tests      .     ,    .         , 

39 

Rough  microstructure  examina- 
tion    •'•  1        .         .         . 

40 

Repeat  stresses         ,        .    '     . 

41 

Combined  bending  and  torsion 

42 

Combined    torsion   and   direct 
stresses          .... 

43 

Tests  on  balls   . 

44 

Hardness  tests  .         ,        •.    '     . 

45 

Comparison  of  tensile  strength 
and  hardness  .... 

46 

Testing  thick  cylinder 

47 

Timber  test  in  tension 

T.M. 


226  A  HANDBOOK  OF  TESTING  MATERIALS 

TABLE  XXXII.— Continued. 


Experi- 
ment No. 

Description  of  Experiment. 

Set  by. 

Date. 

Examined 
by. 

Date. 

48 

Timber  test  -crushing  test 

49 

Shear  test  on  short  beams 

50 

Testing  of  long  timber  beams  . 

I       * 

51 

Testing  of  long  timber  struts  . 

52 

Specific  gravity  of  cement 

53 

Time  of  setting  test  . 

54 

Tensile  tests  with  cements,  etc. 

55 

Compression  tests         ,,          ,, 

• 

56 

Soundness  tests  of  cements 

57 

Compressiye  tests  on  stones     . 

58 

Tests  on  ferro-  concrete  beams  . 

59 

Tests  on  wood-concrete  beams  . 

APPENDIX    I. 


STANDARD    RESULTS   OF   TESTS   ON   THE   STRENGTH   OF 

MATERIALS. 

THE  following  tables,  taken  from  various  sources,  give  the  results 
obtained  on  various  materials  and  will  indicate  the  kind  of  results  to  be 
expected  in  practice.  It  will  be  found  on  comparison  of  results  from 
different  sources  that  there  are  often  wide  differences  ;  from  which  it 
will  be  seen  that  in  all  important  machines  and  structures,  where  the 
material  is  to  be  used  in  the  most  economical  manner,  it  is  essential  that 
samples  and  specimens  of  the  actual  material  employed  should  be  tested 
and  under  as  near  the  conditions  of  use  as  is  possible  in  the  testing 
laboratory. 

TESTS  IN  TENSION,  TORSION,  AND  SHEAR  ON  THE  CHIEF  MATERIALS 
OF  CONSTRUCTION.1 

TABLE  XXXIII.— TENSION. 


Material. 

Specimen. 

Elastic  Limit. 
Lbs.  per  sq.  in. 

Breaking  Stress. 
Lbs.  per  sq.  in. 

Wrought  iron,  Nether-  ( 
ton  Crown  best.         ( 

1 

2 

31,970 
35,550 

47,950 

48,850 

Bessemer  steel. 

1 
2 

69,760 
70,700 

116,930 
108,550 

Crucible  steel. 

1 
2 

67,500 

71,680 

113,020 
120,680 

Rivet  steel. 

I 
2 

40.000 
40,190 

65,500 
62,630 

Crown  rivet  iron.        j 

1 
2 

37,500 
37,970 

56,700 
55,300 

Cast  iron,  skin  on. 

1 
2 
3 



28,310 
22,140 
26,380 

Cast    steel    (cut    from  ( 
casting).               ( 

1 
2 

38,350 

38,870 

85,700 
84,850 

1  Proc.  Inst.  Civ.  Eng.,  vol.  xc.,  pp.  396 — 407. 


Q  2 


228 


APPENDIX  I. 


TABLE  XXXIII.—  TENSION— Cvon£«//  //<•< /. 


Material. 

Specimen. 

Elastic  Limit. 
Lbs.  per  sq.  in. 

Breaking  Stress. 
Lbs.  per  sq.  in. 

Cast  steel,  in  compres-  j 
stow.                   ( 

1 
2 

39,010 
39,860 

— 

Siemens-Martin  steel,    j 

1 

9 

37.060 
35,760 

57,500 
57,900 

Wrought  iron,  S.C.     ( 
Crown.                 ( 

1 

2 

38,260 
38,490 

54,330 
55,690 

Muntz  metal  bar. 

1 
2 

25,000 
25,000 

57,500 
56,540 

Gunmetal,  Cu.  64  parts,  ( 
Sn.  8,  Zn.  2  parts.      ( 

1 
»> 

17,500 
15,000 

29,070 
32,380 

TABLE  XXXIV.— TORSION. 


Material. 

Specimen. 

Elastic  Limit, 
Lbs.  per  sq.  in. 

Breaking  Stress. 
Lbs.  per  sq.  in. 

"W  rought  iron,  Nether-    \ 
ton  Crown  best.          j 

1 
2 
3 

20,560 
18,700 
18,900 

57,800 
54,900 
56,600 

Bessemer  steel. 

1 
2 
3 

46,400 
45,400 
44,500 

101,000 
99,460 
99,550 

Crucible  steel. 

1 
2 
3 

43,100 
43,600 
43,300 

97,900 
90,000 
96,800 

Landore  rivet  steel. 

1 
2 
3 

37,200 
23,200 
22,400 

78,700 
66,840 
67,100 

Netherton  Crown  rivet   j 
iron.                    | 

1 
2 

3 

22,950 
21,600 
25,200 

64,700 
64,700 
64,600 

APPENDIX  I. 


229 


TABLE  XXXV.— TORSION—  Continued. 


Material. 

Specimen. 

Elastic  Limit. 
Lbs.  per  sq.  in. 

Breaking  Stress. 
Lbs.  per  sq.  in. 

Cast  steel. 

1 
2 

3 

24,300 
23,500 
22,400 

78,200 
78,250 
77,000 

Siemens  Martin  steel,  j 

1 
2 
3 

24,200 
21,800 
21,800 

65,300 
63,000 
60,600 

Wrought  iron,  S.C.      \ 
Crown.                | 

1 
2 
3 

22,950 
22,100 
23,700 

67,400 
62,700 
68,400 

Muntz  metal. 

1 
2 
3 

19,700 
19,200 
19,700 

59,000 
57,600 
59,000 

Gun-metal,  Cu.  64,      ( 
Zn.  2,  and  Sn.  8  parts.    ) 

1 
2 
3 

12,100 
12,100 
12,100 

33,800     , 
36,500 
36,200 

Cast  iron  ;  Turned.      1  ( 
part  Dalmelington,  6  j 
parts  best  scrap.          ( 

Highest 
Lowest 
Mean  of  Six 

— 

40,100 
28,450 
33,040 

Cast  iron,  skin  on. 

1 
•> 

3 

— 

46,800 
36,600 
38,500 

Cast  iron  ;    Turned,     1  <' 
part    Sunder]  and,    3  J 
parts  best  scrap.          \ 

Highest 
Lowest 
Mean  of  Six 

— 

41,800 
33,900 
38,200 

Cast  iron.     Skin  on.    < 

Highest 
Lowest 
Mean  of  Five 

— 

37,500 
32,150 
34,330 

230 


APPENDIX  I. 


TABLE  XXXYI. — SHEAR  on  "  RIVET"  TESTS. 


Material. 

Specimen. 

Shear 
Strength. 
Lbs.  per 
sq.  in. 

Material. 

Specimen. 

Shear 

Strength. 
Lbs.  per 
sq.  in. 

Wrought  iron,  / 
Netherton     \ 
Crown            / 
best 

Highest 
Lowest 
Mean  of  6 

44,350 
40,000 
42,050 

Wrought-         i 
iron,  S.C. 
Crown 

Highest 
Lowest 
Mean  of  5 

46,950 
46,030 
46,510 

Muntz         ( 
metal          | 

Highest 
Lowest 
Mean  of  6 

42,860 
40,270 
42,000 

Bessemer       \ 
steel           | 

Highest 
Lowest 
Mean  of  6 

81,910 
76,780 

78,880 

Gunmetal,        / 
Cu.  64, 
Sn.  8,            j 
Zn.  2  parts 

Highest 
Lowest 
Mean  of  6 

30,650 
22,630 
27,960 

Crucible        I 
steel           | 

Highest 
Lowest 
Mean  of  6 

76,200 
73,500 
74,500 

Landore  rivet  ) 
steel           f 

Highest 
Lowest 
Mean  of  4 

53,180 
50,540 
51,570 

Cast-iron.          r 
Turned.        \ 
Dalmeling-  / 
ton,  1.  Best  \ 
scrap  5          / 
parts 

Highest 
Lowest 
Mean  of  11 

13,860 
10,280 
11,860 

Netherton      ( 
Crown  rivet 
iron 

Highest 
Lowest 
Mean  of  G 

48,800 
47,160 
47,870 

C.I.    Turned. 
Sunder-        ( 
land,  1. 
Best  scrap,  f 
3  parts 

Highest 
Lowest 
Mean  of  12 

! 

13,740 
9,280 
11,420 

Cast  steel 

Highest 
Lowest 
Mean  of  5 

63,520 
58,720 
60,160 

Siemens-       i 
Martin  steel    i 

Highest 
Lowest 
Mean  of  5 

48,300 
45,850 
46,910 

Ditto,  ditto.      ( 
Skin  on        j 

Highest 
Lowest 
Mean  of  6 

13,920 
6,740 
8,810 

APPENDIX  I. 


231 


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APPENDIX  I. 


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8,792,000  (WO 
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APPENDIX  I. 


233 


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APPENDIX    II. 


ADMIEALTY    EULES  FOR   TESTING   MATERIALS    FOR 
MACHINERY. 

1.  Steel  Castings  for  Machinery. — Steel  castings  for  the  machinery 
are  to  satisfy  the  following  conditions  : — Tensile  strength,  not  less  than 
28  tons  per  sq.  inch,  with  an  extension  in  2  inches  of  length  of  at  least 
23  per  cent.     Bars  of  the  same  metal,  1  inch  square,  should  be  capable 
of  bending  cold,  without  fracture,  over  a  radius  not  greater  than  1§ 
inches,  through  an  angle  depending  on  the  ultimate  tensile  strength, 
this  angle  to  be  not  less  than  90°  at  28  tons  ultimate  strength,  and  not 
less  than  60°  at  35  tons  ultimate  strength  and  in  proportion  for  strength 
between  these  limits.      For  intricate    thin  castings  the  extension  in 
2  inches  of  length  is  to  be  at  least  10  per  cent. ;  and  the  bending  angle  is 
to  be  not  less  than  20°  at  28  tons  ultimate  strength,  and  15°  at  35  tons 
ultimate  strength,  and  in  proportion  for  strengths  between  these  limits. 
Test  pieces  are  to  be  taken  from  each  casting.     All  steel  castings  are 
also  to  satisfactorily  stand  a  falling  test,"  the  articles  being  dropped  from 
a  height  of  12  feet  (or  as  may  be  approved)  on  a  hard  macadamised  road 
or  a  floor  of  equivalent  hardness. 

It  is  to  be  distinctly  understood  that  contractions  or  defects  in  steel 
castings  are  not  to  be  made  good  by  patching,  burning,  or  by  electric 
welding,  without  the  sanction  of  the  Admiralty  overseers. 

2.  Steel  Forgings  for  Machinery. — All  steel  forgings  are  to  satisfy 
the  following  conditions  :  Ultimate  tensile  strength,  not  less  than  28  tons 
per  sq.  inch,  with  an  extension  in  2  inches  of  length  of  at  least  30  per 
cent.     Bars  of  the  same  metal,  1  inch  square,  should  be  capable  of  being 
bent  cold,  without  fracture,   through  an    angle  of    180°  over  a  radius 
not  greater  than  ^  inch.     Test  pieces  are  to  be  taken  from  each  forging. 
Crank  and  propeller  shafts  are  to  have  test  pieces  taken  from  each  end, 
and  the  ultimate  tensile  strength  of  the  material  of  these  shafts  must 
not  exceed  32  tons  per  square  inch. 

For  all  important  forgings,  such  as  crank  and  propeller  shafts, 
connecting  and  piston  rods,  the  forgings  are  to  be  gradually  and  uniformly 
forged  from  solid  ingots,  from  which  at  least  30  per  cent,  of  the  top  end 
of  the  ingot  has  been  removed  before  forging,  and  at  least  3  per  cent,  of 
the  total  weight  of  the  ingot  from  the  bottom  end  after  forging.  The 
sectional  area  of  the  body  of  the  finished  forging  is  to  be  not  more  than 
J  the  original  sectional  area  of  the  ingot. 


APPENDIX  II.  235 

3.  Cast  Iron. — Test  pieces  to  be  taken  from  such  castings  as  may  be 
considered  necessary  by  the  inspecting  officer.      The  minimum  tensile 
strength  to  be  9  tons  per  sq.  inch,  taken  on  a  length  of  not  less  than  2 
inches.     The  transverse  breaking  load  for  a  bar  1  inch  square,  loaded  at 
the  middle  between  supports  1  foot  apart,  is  not  to  be  less  than  2,000  Ibs. 

4.  Gun-metal,  Naval  Brass,  and    White  Metal. — The  gun-metal 
used  for  all  castings  throughout  the  whole  of  the  work  supplied  by  the 
contractors  is,  unless  otherwise  specified,  to  contain  not  less  than  8  per 
cent,  of  tin,  and  not  more  than  5  per  cent,  of  zinc,  the  remainder  to  be  of 
approved  quality  copper ;  the  exact  proportion  of  tin  above  8  per  cent, 
being  arranged  as  may  be.required,  depending  on  the  use  for  which  the 
gun-metal  is  intended.     The  ultimate  tensile  strength  of  gun-metal  is  to 
be  not  less  than  14  tons  per  sq.  inch,  with  an  extension  in  2  inches  of 
length  of  at  least  7^  per  cent.     The  composition  of  any  naval  brass  used 
is  to  be  :  Copper,  62  per  cent. ;  zinc,  37  per  cent. ;  and  tin,  1  per  cent.   All 
naval  brass  bars  are  to  be  cleaned  and  straightened.      They  are  to  be 
capable  of  (1)  being  hammered  hot  to  a  fine  point,  (2)  being  bent  cold 
through  an  angle  of  75°  over  a  radius  equal  to  the  diameter  or  thickness 
of  the  bars.     The  ultimate  strength  of  naval  brass  bars  f  inch  diameter  and 
under   is  not  to  be  less  than  26  tons  per  sq.  inch,  and  for  round  bars 
above  f  inch  diameter,  and  square  bars  not  less  than  22  tons  per  sq.  inch, 
whether  turned  down  in  the  middle  or  not.     The  extension  in  2  or  4 
inches  of  length  is  to  be  at  least  10  per  cent.     Breaks  within  ^  inch  of 
the  grip  are  not  to  count.      Cuttings    from  the  propellers  and   other 
important  gun-metal  castings   and  naval  brass  work  will  be  sent  to 
Portsmouth  Dockyard  for  analysis.     The  white  metal  used  for  bearing 
surface  is  to  contain  at  least  85  per  cent,  of  tin,  not  less  than  8  per  cent, 
of  antimony,  and  about  5  per  cent,   of  copper ;  zinc  or  lead  should  not 
be  used.     The  brasses  are  to  be  carefully  tinned  before  filling  with  white 
metal. 

5.  Copper  for  Pipes. — Strips  cut  from  the  steam  and  other  pipes,  either 
longitudinally  or  transversely,  are  to  have  an  ultimate  tensile  strength  of 
not  less  than  13  tons  per  sq.   inch  when  annealed  in  water,    with  an 
elongation  in  a  length  of  2  inches  or  4  inches  of  not  less  than  35  and  30 
per  cent,  respectively.     Such  strips  are  also  to  stand  bending  through  180° 
cold  until  the  two  sides  meet,  and  of  hammering  to  a  fine  edge  without 
cracking. 


APPENDIX    III. 


RESEARCHES  ON   COMBINED    STRESS.1 

Ix  engineering  design  it  frequently  happens  that  the  material  is 
simultaneously  subjected  to  more  than  one  single  stress,  and  in  this  case 
the  material  is  said  to  be  subjected  to  combined  stresses.  Probably  the 
most  discussed  instance  of  a  case  of  this  nature  occurs  in  the  combined 
bending  and  twisting  of  a  crank-shaft ;  but  to  explain  the  gist  of  the 


PIG.  125. — Section  of  Specimen  under  Compound  Stress. 

matter  in  a  lucid  way — so  that  those  not  previously  conversant  with  the 
subject  can  appreciate  it  readily — we  will  first  consider  the  case  of  a 
boiler  without  longitudinal  stays. 

Taking  a  small  square  (see  Pig.  125)  at  the  surface  A  B  C  D,  we  know 
that  if  A  B  and  C  D  lie  along  the  length  of  the  boiler,  then  the  surface 
A  B  b  a  (where  a  b  c  d  is  the  inside  surface  with  A  B  C  D)  is  subjected  to 
a  tension  hoop  stress  2  p,  and  the  surface  B  C  c  &  is  subjected  to  a  length- 
ways tension  stress  p,  as  a  result  of  the  pressure  inside  the  boiler.  Thus 
the  material  is  subjected  to  the  combined  stresses  2  p  andj?,  both  being 

1  This  has  been  compiled  from  various  contributions  by  the  author  to 
Engineering  and  papers  which  have  been  read  on  the  subject  before  technical 
societies. 


APPENDIX  III.  237 

tensile.  There  is  also  a  third  stress,  of  varying  amount,  acting  radially  ; 
but  as  this  is  at  most  only  equal  to  the  boiler  pressure,  we  shall  omit  it 
for  the  sake  of  clearness. 

Now,  if  we  had  the  material  of  the  boiler  under  the  hoop  stress  2  p 
only,  we  should  know  what  factor  of  safety  the  boiler  would  have,  or 
what  internal  pressure  it  would  stand  without  yielding,  if  we  had  made  a 
test  of  the  material  in  an  ordinary  testing  machine.  But  when  in 
addition  to  this  hoop  tension  2  p  we  have  a  second  stress  p  simultaneously 
applied  at  right  angles  to  it,  the  question  arises  as  to  what  effect  it  will 
have  on  the  capability  of  the  material  to  withstand  the  larger  hoop 
stress. 

It  is  evident  that  the  direct  experiment  in  the  testing-machine  will 
not  tell  us  this  ;  it  applies  one  simple  tension  only. 

The  stress  we  are  concerned  with  is  the  yield-point  stress  —  i.e.,  the 
stress  at  which  rapid  permanent  change  of  shape  takes  place.  This  stress 
is  now  used  as  the  basis  in  strength  calculations,  in  place  of  the  formerly 
used  "  ultimate  strength." 

A  full  discussion  of  the  various  theories  which  have  been  advanced  for 
the  failure  of  materials  under  combined  stress  would  be  out  of  place  in 
this  book,  and  the  reader  should  refer  to  the  numerous  papers  before  the 
technical  institutions  and  articles  in  the  technical  papers  by  Guest  and 
others  on  this  subject.1 

It  will  suffice  to  say  here  that  the  tendency  of  modern  research  has 
been  to  demonstrate  that  for  ductile  materials  such  as  mild  steel  failure 
under  combined  stress  takes  place  when  the  maximum  shear  stress 
reaches  a  definite  value,  this  shear  stress  being  half  the  algebraic  sum  of 
the  principal  stresses.  Or,  expressed  in  symbols, 

If  p  is  the  direct  stress,  and  q  the  shear  stress  at  right  angles  — 


Maximum  shear  stress= 


l^ 

=     /^- 


The  two  principal  stresses  being  ^  -i-*/^z+f  and  —  ^ 

This  failure  under  maximum  shear  stress  has  been  aptly  termed  Guest's 
Law.  The  first  experimenter  to  carry  out  research  work  in  this  direction, 
which  can  be  taken  to  give  a  reliable  basis  for  deduction,  was  Mr.  J.  J. 
Guest.  The  following  description  will  indicate  the  method  employed. 

He  arranged  his  tests  upon  hollow  tubes,  which  he  could  subject  to 
tension,  torsion,  and  to  internal  fluid  pressure  ;  he  thus  obtained  a  series 
of  varied  combined  stresses,  from  which  the  law  given  above  was  first 
deduced.  The  value  of  this  indirect  method  is  proved  by  the  definite 
success  of  the  investigation. 

The  specimen  is  placed  in  an  ordinary  single-lever  testing  machine, 

1  See  Bibliography  at  end. 


238  APPENDIX  III. 

but  between  the  specimens  and  the  jaws  of  the  machine  are  ball-bearings 
which  would  allow  the  specimen  to  turn  easily  while  under  the  load 
of  the  testing  machine.  A  bar  passed  through  the  top  of  the  specimen 
served  to  apply  the  torque,  a  pair  of  bands  running  from  the  bar  over 
pulleys,  and  were  attached  to  another  bar,  to  the  centre  of  which  loads 
were  applied  to  produce  the  torque.  The  bottom  of  the  specimen  was 
prevented  from  turning  by  a  bar  which  pressed  against  stops.  The  piping 
by  which  the  fluid  under  pressure  was  applied  to  the  interior  of  the 
specimen  was  used  only  in  certain  of  the  tests.  The  pressure  in  the  piping 
was  measured  by  a  gauge.  The  specimens  were  tubes  (of  steel,  brass,  and 
copper),  soldered  on  to  holders  at  each  end,  and  tension  loads,  torques,  or 
internal  fluid  pressure  were  applied,  both  singly  and  in  various  combina- 
tions of  two  at  a  time. 

To  measure  the  strains  and  determine  the  yield-points  in  the  various 
tests  two  instruments  were  used — namely,  an  extensometer,  to  measure 
the  length  extension  of  the  specimen,  and  a  torsion-meter.  Both  were 
optical  instruments.  The  extensometer  gave  the  mean  axial  extension, 
and  was  not  affected  by  any  bending  or  twisting  of  the  specimen,  and  the 
tests  of  its  accuracy  indicated  an  extreme  error  of  strihny  in-  only- 
The  torsion-meter  seems  to  have  also  been  exceedingly  accurate.  Both 
instruments  were  "  single  reading" — that  is,  only  one  observation  had  to 
be  taken  to  obtain  the  extension  or  twist  on  the  specimen,  and  this 
evidently  is  of  importance  in  determining  yield-points. 

Nine  steel  tubes  were  experimented  upon,  involving  101  different  tests; 
each  tube  was  experimented  upon  several  times,  the  stress  being  taken 
off  when  the  yield-point  had  been  reached  in  any  test.  To  explain  the 
system  of  testing  we  will  take  the  eet  of  nine  tests  on  tube  No.  4  and 
examine  them. 

The  first  test  was  a  torsion  test.  A  small  load  torsion  of  250  Ibs.  was 
put  on  a  specimen  to  steady  it.  The  loads  producing  the  torque  were  then 
applied  by  uniform  amounts  and  the  twists  of  the  specimen  observed  at 
each  addition.  On  approaching  the  yield-point  loads  would  be  added 
more  gradually,  and  the  twist  carefully  watched  for  any  continued 
yielding  under  a  constant  load.  When  this  occurred,  or  the  change  of 
twist  readings  ceased  to  be  proportional  to  the  added  load,  the  yield-point 
would  have  been  reached,  and  owing  to  the  thinness  of  the  tubes  this 
would  be  cleaily  denned.  It  occurred  at  a  load  of  90  Ibs.  The  shearing 
stress  was  then  22,500  Ibs.  per  sq.  inch.  The  load  was  then  removed. 
The  next  test  was  a  tension  test ;  in  this  case  the  extensometer 
readings  were  taken  and  the  yield-point  found  to  occur  at  a  load  of 
4,000  lb.,  or  a  tensional  stress  of  41,200  Ibs.  per  sq.  inch.  The  third  test 
is  a  combined  torsion  and  tension  test.  The  specimen  was  first  gradually 
loaded  with  a  torque  load,  and  the  twist  read,  but  when  70  Ibs.  had  been 
applied  this  loading  was  stopped  and  the  tension  load  increased.  Both 
the  twist  and  the  extension  would  have  been  read  as  these  loads  were 
added,  and  the  twist  reading  should  not  change  until  the  yield-point 


APPENDIX  III.  239 

is  reached,  which  occurred  at  a  load  of  2,750  Ibs.,  when  the  specimen  would 
slowly  yield,  both  by  extending  and  by  twisting,  although  no  addition 
was  made  to  the  torque.  The  principal  stresses  would  be  calculated  from 
the  tension  load  and  torque  combined.  They  were  38,650  Ibs.  per  sq. 
inch  tension  and  8,350  Ibs.  per  sq.  inch  compression. 

The  fourth  test  was  a  combined  tension  and  internal  pressure  test. 
In  this  case  the  tension  load  was  added  first,  readings  of  the  extensometer 
being  taken  to  make  sure  that  everything  was  working  rightly.  At  a 
load  of  3,000  Ibs.  this  was  kept  constant,  and  the  further  stresses  added  by 
applying  internal  fluid  pressure  and  gradually  increasing  it.  When 
this  fluid  pressure  was  1,150  Ibs.  per  sq.  inch  the  tube  began  to 
yield,  both  by  stretching  and  increasing  in  diameter,  and  the  loads  were 
removed. 

Test  No.  5  was  a  torsion  and  internal  pressure  test ;  the  torsion  load 
was  applied  first  to  the  amount  produced  by  75  Ibs.,  and  then  the  internal 
fluid  pressure  was  applied. 

Guest,  when  testing  these  tubes  under  combined  tension  and  internal 
pressure,  made  due  allowance  for  the  increase  of  tension  (longitudinal) 
due  to  the  internal  pressure.  The  tubes  were  sealed  at  the  ends.  In 
order  to  obtain  the  actual  axial  stress  at  any  time,  the  axial  stress  p\  due 
to  the  internal  pressure  was  added  to  the  axial  stress  pQ  due  to  the  tension 
load  on  the  machine.  The  actual  axial  stress  was  thus  pi  +  Po,  and  the 
circumferential  stress  2  pi.  This  is  clearly  stated  by  Guest  in  that  section 
of  his  paper  entitled  "The  Calculation  of  Stresses,"  and  it  is  evident 
that  if  the  specimens  are  definitely  closed  at  the  ends,  then  the  actual 
stress  is  obtained  by  adding  together  the  stresses  due  to  the  tension 
load  and  to  the  internal  pressure.  For  tube  No.  7,  e.g.,  there  were  two 
tests.  In  the  first  test  the  tube  yielded  to  circumferential  stress,  and  in 
the  second  to  axial  stress — the  amounts  of  the  stresses  being  interchanged. 
The  results  showed  that  the  material  was  isotropic ;  tests  on  two  other 
tubes  confirmed  this. 

Some  diagrams  plotted  from  these  three  kinds  of  combined  tests  are 
given  by  Guest,  and  they  give  two  strain  readings  and  the  load  readings, 
and  so  represent  the  whole  test  very  clearly.  The  material  always 
appears  to  yield  in  the  two  ways  simultaneously. 

Test  No.  6  was  similar  to  No.  4,  No.  7  to  No.  3,  No.  8  to  No.  2,  and 
No.  5  to  No.  1. 

Considering  the  maximum  principal  (tensional)  stresses  at  the  yield- 
point,  we  see  that  these  varied  from  22,500  Ibs.  per  sq.  inch  in  a  torsion 
test  to  42,900  Ibs.  in  a  tension  and  internal  pressure  test,  or  to  41,200  Ibs. 
per  sq.  inch  in  the  simple  tension  test.  These  quantities  are  in  the  ratio 
of  1  to  1-91  and  1-86. 

Taking  the  maximum  yield-point  shearing  stresses  in  the  various 
experiments,  these  vary  from  20,200  Ibs.  per  sq.  inch  in  the  torque  and 
internal  pressure  test  to  22,500  Ibs.  per  sq.  inch  in  the  simple  torsion  test, 
and  these  quantities  are  in  the  ratio  of  1  to  I'll. 


240 


APPENDIX  III. 


TABLE  XXXIX. — TABULATED  RESULTS  OF  SOME  OF  GUEST' 
EXPERIMENTS  ON  STEEL  TUBES. 

Mean  diameter  =  1*250  in. 

Thickness  =  0-025  in. 

Young's  modulus  (E)  =  31,100,000  Ibs.  per  sq.  in. 

Modulus  of  rigidity  (K)  =  11,170,000  Ibs.  per  sq.  in. 

Poisson's  ratio  (<r)  =  0*393. 

P  =  testing-machine  load  in  Ibs.  weight. 

W  =  load-producing  torque. 

Po  =  Internal  pressure  in  Ibs.  per  sq.  in. 


Applied 
Loads. 

Principal 
Stresses. 

Elongation. 

Test 

Max. 

No. 

Shear. 

P. 

w. 

Po- 

Pi- 

Jfe 

Experi- 
mental. 

Cal- 
culated. 

1 

_ 

90 

_ 

22,500 

-22,500 

22,500 

0-001035 

0-001005 

2 

4000 

— 

— 

41,200 

0 

20,600 

0-001385 

0-001325 

3 

2750 

70 

— 

38,650 

-  8,350 

22,500 

0-001425 

0-001350 

4 

3000 

— 

1150 

42,900 

24,000 

22,000 

0-001075 

0-001078 

5 

—  . 

to 

1150 

37,700 

-   1,700 

20,200 

0-001250 

0-001235 

6 

2500 

— 

1600 

42,700 

33,800 

22,100 

0-000940 

0-000925 

t 

3400 

50 

— 

39,000 

—  4,000 

21,500 

0-001324 

0-001305 

8 

4000 

— 

— 

41,200 

0 

20,600 

0-001388 

0-001325 

9 

— 

90 

— 

22,500 

—22,500 

22,500 

0-001070 

0-001005 

The  greatest  extension  at  the  yield-point  may  be  arrived  at  in  two 
ways ;  first,  by  taking  the  readings  of  the  measuring  instruments,  and 
hence  obtaining  the  extensions;  or,  secondly,  by  calculating  the  exten- 
sion from  the  stresses  and  the  previously  measured  elastic  constants  of 
the  material.  The  first  method  has  the  advantage  of  being  more  directly 
experimental ;  but  as  the  material  will  have  suffered  permanent  stretching 
before  the  yield- point  is  definitely  determined,  it  is  hardly  so  fair  a  com- 
parison as  the  second  method.  Taking  the  second  method,  the  limiting 
extension  varies  from  0*000925  in  the  second  tension  internal  pressure 
test  and  0*001005  in  the  simple  torsion  test  to  0*001325  in  the  simple 
tension  test.  These  are  in  the  ratios  of  1  :  1-09  :  1  43. 

The  difference  from  constancy  is  nearly  four  times  as  great  in  the 
extension,  and  eight  times  us  great  in  the  principal  stress  as  it  is  in  the 
shearing  stress.  In  the  tests  on  the  other  tubes  similar  results  were 
obtained,  and  Guest  hence  propounded  the  law  that  the  shearing  stress 
was  constant,  as  being  sufficiently  accurate  for  engineering  purposes, 
although  he  sets  forth  a  nearer  approximation  should  it  be  required  for 
scientific  purposes. 

Besides  the  work  of  Guest  several  experimenters  have  since  carried  out 
work  in  the  same  direction. 


APPENDIX  III. 


241 


In  America,  Professor  Hancock  has  carried  out  an  elaborate  series  of 
tests  on  steel  tubes,  a  resume  and  criticism  of  which  was  contributed  by 
the  author  to  Engineering,  August  20, 1909.  These  tests  give  results  which 
cannot  be  said  to  prove  any  of  the  theories  at  present  enunciated.  The 
following  table  compiled  from  the  results  published  will  indicate  this : — 


TABLE  XL. 


Average  Variation  from  Mean  per  cent. 

Specimens. 

—  +/V/  —  +q%. 

\/P~-+  2 

Principal 

' 

Strain. 

Eankine. 

Guest. 

St.  Venant. 

Nickel  steel,  solid  round 

11-2 

13-1 

7:7 

Low  carbon  steel,  solid  rounds 

7 

20 

7 

Steel  tubing  1  in.  outside  diameter, 
0*075  in.  inside  diameter 

10-3 

11-5 

6-1 

Steel  tubing  1  in.  outside  diameter, 

0-05  in.  thick       .... 

13-8 

5-2 

8-7 

Steel  tubing  1  in.  outside  diameter, 

0*25  in.  thick       .... 

8-5 

11-2 

•  7-8 

Low-  carbon  compression  torsion    . 

6-7 

16-2 

4-7 

Average  of  all  tests 

9-6 

12-9 

7 

Mr.  "Walter  Scoble  has  attempted  to  solve  the  problem  by  conducting 
tests  on  a  material  subjected  to  combined  bending  and  twisting.  It  is  a 
pleasure  to  be  able  to  say  that  this  work  has  been  conducted  in  a  very 
scientific  manner.  The  following  criticism  refers  only  to  the  experiments 
on  ductile  materials  under  combined  stress.  His  work  on  brittle  materials 
is  mentioned  later. 

The  great  difficulty  which  Mr.  Scoble  encountered  was  the  location 
of  yield-points.  He  very  ingeniously  attempted  to  obtain  a  fixed  point 
for  the  yield.  He  found  a  decided  elastic  limit  effect  during  all  these 
tests,  which  he  attributed  to  local  yielding.  He  says1 : — "  If  the  material 
is  satisfactory,  the  stresses  at  the  elastic  limit  and  yield-point  are  nearly 
proportional,  and  it  makes  little  difference  which  is  taken.  Faulty 


Philosophical  Magazine,  vol.  xii..  p.  535. 


T.M. 


242 


APPENDIX  III. 


specimens  will  usually  have  a  low  elastic  limit,  whereas  the  yield-point  is 
little  affected,  and  the  same  applies  to  changes  in  the  metal  due  to  any 
special  treatment  to  which  it  may  have  been  subjected.  Taking  these 
facts  together,  it  is  evident  that  the  yield-point  is  much  more  nearly 
constant  than  the  elastic  limit,  and  in  making  a  simple  test  it  is  correct  to 
consider  both  points  in  relation  to  each  other."  With  this  probably  all 
experimenters  will,  be  in  complete  agreement ;  the  point  of  disagreement 
will  be  in  the  accurate  determination  of  the  yield-point.  In  Mr.  Scoble's 
experiments  there  was  more  difficulty  in  getting  a  clearly-defined  yield- 


Assume  d 
Yield  Pt. 


Eac  tension 
PIG.  126.— W.  Scoble's  Method  of  deciding  Yield-Point. 


point  than  when  the  material  is  loaded  in  direct  torsion,  or  compression 
and  torsion,  because  of  the  varying  stress  due  to  bending,  as  well  as  to 
torsion.  It  is  true  that  his  ingenious  arrangement  enables  the  same 
stresses  to  be  obtained  with  smaller  forces,  but  providing  that  the  apparatus 
is  available  for  a  fairly  uniformly  distributed  stress,  it  would  appear  more 
satisfactory  to  leave  out  the  additional  complication  obtained  during  a 
bending  test.  What  is  doubtful  is  whether  Mr.  Scoble  did  obtain  the  real 
yield-point.  His  method  is  indicated  in  Fig.  126.  He  himself  remarked 
concerning  this  method,  "  supposing  this  course  was  not  justified,  at  least 
this  is  a  definite,  easily  determined  point  to  deal  with,  and  any  probable 
error  would  not  be  greater  than  that  which  is  likely  to  arise  when 
taking  a  point  less  closely  defined."  It  is  clear  that  he  is  not  fully 
satisfied  with  this  determination  of  yield-point. 


APPENDIX  III. 

A  table  of  results  obtained  by  Mr.  Scoble  is  given  below  :— 

TABLE  X LI.— RESULTS  OBTAINED  BY  ME.  SCOBLE. 
(Combined  Bending  and  Torsion.) 


243 


Number  of 

p             /p2 

/J92 

Tests. 

P' 

?• 

~2     VT+' 

V7  q' 

I. 

64,600 

0 

64,600 

32,300 

III. 

0 

29,170 

29,170 

29,170 

IV. 

16,220 

28,250 

37,500 

29,400 

V. 

32,350 

25,750 

48,200 

32,000 

VI. 

48,600 

23,050 

57,800 

33,500 

VII. 

58,750 

14,240 

61,980 

32,600 

XII. 

48,600 

20,900 

56,740 

32,440 

VIII. 

62,100 

7,840 

63,080 

32,030 

IX. 

56,100 

16,220 

60,450 

32,400 

XI. 

35,330 

24,700 

48,060 

30,400 

Average  variation  from,  mean  of  maximum  shear  stress  =  3*72  per  cent. 

It  will  be  seen  that  in  this  case  we  have  for  the  average  variation  from 
the  mean  for  the  whole  of  the  tests  : — Maximum  shear  stress  =  3 '72  per 
cent.,  maximum  principal  stress  =  18'3  per  cent.  A  study  of  the  above 
facts  reveals  considerable  evidence  in  favour  of  Guest's  law  for  combined 
tension  and  shear  stresses,  and,  but  for  the  disturbing  influence  of 
Professor  Hancock's  experiments,  this  would  satisfy  many  engineers. 
At  the  same  time,  we  must  bear  in  mind  that  if  any  general  law  for  the 
failure  of  all  materials  is  to  be  ascertained  the  results  must  include 
compression  as  well  as  tension  data.  Taken  in  conjunction  with  the 
results  obtained  by  Guest,  Scoble's  experiments  show  that  for  design 
purposes  Guest's  law  is  true.  So  far,  then,  we  have  three  experimenters 
who  have  published  results ;  all  three  express  opinions  in  favour  of 
Guest's  law,  and  two  of  them  produce  evidence  in  its  favour.  It  is 
probable  that,  in  connection  with  these  tests,  the  engineer  who  has  not 
attempted  to  conduct  similar  work  underrates  the  difficulties. 

It  now  remains  to  deal  with  the  four  points  of  great  importance  in  all 
testing  work,  and  which  has  possibly  had  an  influence  upon  the  results 
obtained  during  the  combined  stress  experiments. 

Max. 


Elastic   Limit  and   Yield-Point,  and  Ratio  of 


Stress. 


Mean 

The  chief  difficulty  arising  under  the  first  heading  is  the  masking  effect 
on  the  elastic  limit  due  to  variation  in  material  and  non-uniformity  of 
stress.  In  any  test  variation  of  material  will  cause  a  greater  variation  in 
elastic  limit  than  in  yield-point.  At  the  true  yield-point  the  "time 
eifect "  is  considerable,  and  the  apparent  yield-point,  if  obtained  by  the 


244 


APPENDIX  III. 


drop  of  the  beam,  is  higher  than  the  true  yield-point.  In  a  tension  or 
compression  test  it  is  essential  to  determine  the  maximum  stress.  The 
ratio  of  the  maximum  to  mean  stress  will,  of  course,  be  much  less  when 
extreme  precautions  have  been  taken  to  ensure  that  the  specimen  is 
loaded  axially.  The  result  of  non-axial  loading  is  shown  to  scale  in 
Fig.  127.  But  whatever  precautions  are  taken,  this  ratio  will  never  be 

10  Tons 


•i 


™~"  """"•"    /   Square     —  — — 


CO 


FIG.  127. — Distribution  of  Stress  in  Specimen  subjected  to  Non-Axial 

Loading. 

unity.  With  spherical  seats,  it  would  at  first  sight  appear  that  an 
axial  load  is  obtained,  but  this  is  by  no  means  the  case,  as  the  results 
given  below  will  show.  Especially  to  be  noted  is  the  author's  test 
A  D,1  which  shows  that  a  most  unaccountable  result  might  have  been 
obtained,  but  for  special  precautions,  when  using  spherical  seats.  It  is 
therefore  essential,  in  order  to  reduce  this  source  of  error  to  a  minimum, 
to  take  measurements  which  will  enable  the  ratio  to  be  calculated.  At 
1  Engineering,  1909. 


APPENDIX  III. 


o 


present  the  only  way  of  doing  this  seems  to  be  by  measuring  strains  in  at 
least  three  planes  round  the  specimen.  Experiments  show  (and  it  can 
be  readily  theoretically  demonstrated)  that  spherical  seats  merely  form  a 
flexible  arrangement  by  which  the  specimen  can  be  placed  approximately 
truly  in  the  machine;  once  the  load  is  applied 
they  do  not  move  but  accommodate  themselves  to 
the  eccentricity  of  loading. 

Variation  of  Material  Used.  —  In  Prof. 
Hancock's  Table  II.  there  are  tests  on  nickel 
steel  solid  rounds.  This  material  is  indefinite 
with  respect  to  its  elastic  limit.  The  low-carbon 
steel  is  stated  to  be  "from  the  same  shipment." 
It  is  possible  that,  although  there  is  little  variation 
in  specimens  off  the  same  bar,  there  is  considerable 
variation  in  specimens  off  the  same  shipment,  as 
there  may  have  been  a  difference  of  temperature 
in  rolling  the  material. 

Time  Effect.  —  The  shape  of  the  curves  given 
by  Prof.  Hancock  leads  one  to  think  that  the 
loading  was  carried  on  at  a  fairly  rapid  rate. 
This  is  undesirable  if  the  exact  elastic  limit  is  to 
be  detected.  Near  the  critical  point  the  time 
influence  is  very  great,  especially  in  torsion  tests, 
and  the  material  will  still  appear  elastic  if  time 
is  .not  allowed  for  the  specimen  to  over-strain. 
The  point  has  been  recently  elaborated  by  the 
author  in  his  paper  before  the  Iron  and  Steel 
Institute.1 

Determination  of  Yield-Point.  —  The  validity 
of  Mr.  Scoble's  method  of  determining  the  yield- 
point  is  based  on  the  assumption  that  the  relation 
of  stress  to  strain  is  still  linear  after  yield  has 
been  passed.  The  time  effect  after  yield  is,  how- 
ever, so  great  that  it  cannot  be  neglected,  and 
the  shape  of  the  curve  does  not  even  approximate 
to  a  straight  line. 

A  number  of  experiments  on  compound  stresses 
have  been  carried  out  by  the  author,  particulars 
of  which  will  be  found  in  papers  read  before  the  Technical  Institutions.2 

Preliminary  experiments  were  made  upon  both  solid  and  tubular  mild 
steel  specimens,  and  it  was  decided  to  use  solid  bars.  In  most  of  the 
author's  experiments  a  specimen  of  1  inch  diameter  was  used.  The 
length  between  the  shoulders  was  4  j  inches.  The  reason  why  similar 
specimens  were  used  for  torsion,  tension,  compression  and  combined 

1  "The  Elastic  Breakdown  of  Certain  Steels,1'  Journal  Iron  and  Steel  Insf., 
No.  1,  1910. 

2  See  Bibliography  at  end. 


XJL 


Lo  cud' 

FIG.  128. — Arrange- 
ment of  Loading 
for  Combined 
Compression  and 
Torsion  Experi- 
ments. 


246 


APPENDIX  III. 


stress  tests  was  that  it  was  desired  to  make  them  interchangeable  for 
elastic  range  tests.  The  ratio  of  the  length  to  the  diameter  was  sufficient 
to  ensure  that,  unless  the  loading  during  a  compression  test  was  placed 
with  considerable  eccentricity,  the  yield -point  in  compression  would  be 
reached  before  the  specimen  failed  as  a  strut.  If  the  loading  is  directly 
through  the  axis  of  the  specimen  it  is  safe  to  make  this  ratio  twenty  for  a 
mild  steel  specimen. 

Previous  experiments  with  various  grips  were  made,  and  as  a  result 
the  specimens  were  turned  with  screwed  ends,  gas-threads  being  used. 
The  general  shape  of  the  specimen  and  the  arrangement  of  the  apparatus 
is  indicated  in  Fig.  128  and  Fig.  129.  The  screwed  ends  were  carefully 


Hull  rare 


FIG.  129. — General  View  of  Combined  Tension  and  Torsion  Apparatus, 
showing  the  Specimen  with  Torsion  Bars  and  Pulleys. 

fitted  to  the  tension  grips  and  the  compression  caps.  The  centre  4^  inches 
of  the  specimen  was  turned  parallel  to  1  in  2,000.  Torque  bars  were 
fastened  by  set-screws  which  fitted  directly  on  to  the  specimen,  at  the 
top  and  bottom,  as  shown  in  Fig.  128. 

A  50-ton  Wicksteed  testing  machine  was  used  for  the  application  of 
tension  and  compression  loads.  Ball-bearings  were  fitted  so  that  the 
specimen  was  free  to  revolve  when  tested  in  torsion. 

The  torque  bars  were  flexibly  coupled  together  and  moved  simul- 
taneously, the  friction  of  the  ball-bearings  being  thus  eliminated  before  a 
reading  was  taken. 

Fig.  129  gives  a  general  idea  of  how  the  torque  was  applied  to  the 
specimen.  The  torque  arms  were  actually  secured  by  means  of  set- 
screws  let  into  countersunk  holes  in  the  specimen.  From  the  end  of 
each  torque  bar  a  cord  was  carried  over  a  bicycle  wheel  and  fastened  to 


APPENDIX  III.  247 

a  knife-edge  upon  which  rested  a  hollow  bar.  A  tray  was  hung  by  a 
knife-edge  on  the  centre  of  this  bar,  and  weights,  marked  W,  were 
placed  in  the  tray  in  order  to  apply  a  torque. 

From  the  arrangements  of  the  pulleys  shown  in  the  sketch  it  will  be 
seen  that  every  effort  has  been  made  to  eliminate  bending  during  the 
application  of  the  torque.  Owing  to  the  longer  distance  between  the 
points  of  support  of  the  specimen,  the  stress  caused  by  bending — due  to 
bad  application  of  the  torsion  load — is  greater  during  a  tension  than 
during  a  compression  test. 

A  probable  source  of  error  in  Mr.  Guest's  experiments  may  now  be 
explained.  He  used  long  torque  bars  at  the  top  end  of  the  specimen, 
and  two  shorter  bars  at  the  bottom  end.  These  two  lower  bars  were 
brought  against  stops.  The  advantage  of  this  arrangement  was  that  it 
was  only  necessary  to  use  one  tray  and  one  set  of  weights,  but  it  is 
probable  that  unbalanced  bending  stresses  are  thereby  set  up  in  the 
specimen,  and  the  arrangement  shown  in  Fig.  129  was  therefore  adopted. 
Strains  were  measured  by  means  of  the  combined  sphingometer  described 
in  Chapter  IV.  for  both  tension  and  torsion.  By  the  use  of  ball-bearings 
in  the  testing  machine  and  the  pulleys  the  effect  of  friction  was  reduced 
to  a  minimum  and  was  negligible.  The  sphingometer  strips  rendered  it 
a  simple  matter  to  record  very  small  strains. 

In  the  experiments  recorded  (SS  specimens)  the  elastic  limit  and  the 
yield-point  coincided.  In  the  case  of  perfectly  homogeneous  specimens 
loaded  in  tension  and  compression  in  such  a  manner  that  the  load 
passes  through  the  axis  of  the  specimen— and  consequently  there  is  no 
bending — the  yield-point  is  marked  by  a  rapid  increase  of  stretch  which 
takes  place  for  a  small  addition  of  load.  The  author's  experiments 
showed  that  the  load  never  is  acting  exactly  through  the  axis  of  the 
specimen.  Some  of  the  material  used  (SS  specimens)  was  remarkably 
homogeneous,1  but  the  load  was  always  slightly  non-axial.  In  such  a 
case  there  will  be  an  apparent  "  elastic  limit  effect  "  if  an  extensometer 
is  used  which  merely  measures  a  mean  extension  of  the  specimen.  With 
non-axial  loading,  and  a  homogeneous  material,  the  yield-point  is 
reached  at  one  portion  of  the  specimen  before  the  whole  of  it  yields. 
With  an  extensometer  which  gives  the  distribution  of  stress,  there  will 
be  an  apparent  rapid  change  in  the  eccentricity  of  loading  directly  any 
portion  reaches  the  yield-point.  Then  will  follow  the  "elastic  limit 
effect"  (during  which  the  mean  extension  of  the  specimen  is  slowly 
increasing  for  equal  increments  of  load)  due  to  eccentric  loading,  and 
then  will  come  the  total  yield  shown  by  a  great  increase  in  strain. 
What  has  been  recorded  in  these  experiments  is  the  maximum  stress  on 
the  specimen  when  the  first  portion  of  it  reaches  the  yield-point. 

Until  the  load  is  reached  at  which  this  portion  yields  there  seems  to  be  no 
"  time  effect,"  but  at  this  point  that  phenomenon  becomes  most  marked. 

The  following  table  (on  page  248)  exemplifies  the  results  obtained : — 

1  The  term  "  homogeneity  "  is  intended  to  include  isotropy  and  uniformity. 


248 


APPENDIX  III. 


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APPENDIX  III. 


249 


Fig.  130  shows  the  results  of  this  table,  together  with  others  obtained 
by  the  author,  plotted  in  a  manner  showing  very  clearly  the  agreement 
with  Guest's  law.  The  latter  would  give  an  exact  circle. 

A  Combined  Stress  Test  fully  worked  out. — Specimen  SS  V,  Test  c. — 
Length  of  specimen  between  points  =  3*903  inches.  Diameter,  T0025 
inch.  Length  of  torque  bars  =  76-4  inches.  Distance  of  sphingometer 
strips  from  axis  of  specimen  =  2-58  inches. 

Calculations  for  Tension  or  Compression  Test. — The  following  readings 
and  calculations  were  made  : — 


Strip  No.  1. 

Strip  No.  2. 

Strip  No.  3. 

Scale  Headings.  Compression  ) 
load  0*5  tons  .  .  .  j 

238 

281 

332 

Scale  Headings.  Compression  ) 
load  3  tons  .  .  .  .  j 

130 

234 

134 

Calibration  equivalent  of  scale  | 
divisions  in  inches  .  .  j 

0-00000776 

0-00000917 

0-00000752 

Extension  of  strips  in  inches  ) 
for  load  of  2'5  tons  .  .  j 

0-000838 

0-000431 

0-001489 

Surface  extension  in  inches    : 

0-000903 

0-000824 

0-001030 

From  the  above  the  mean  extension  =  0 '0009 19  inch,  whence  E  —  30 -2 
x  106  Ibs.  per  sq.  inch. 
The    maximum     surface    extension  1= 0-001041    inch,    whence    ratio 

maximum  stress  ,.     ,  .       1041 

—  on  surface  perpendicular  to  axis=  -——=1-134. 
mean  stress  919 

Torsion  Test. — Calibration  of  torsion  strip  gave  1  division  =  0'00001986 
radians. 

A  compression  load  of  3  tons  was  kept  on  the  specimen  and  the  torque 
applied  by  adding  weights  to  the  trays. 

It  was  found  that  an  increase  of  70  Ibs.  caused  a  deflection   of  447 
divisions. 

0-501 X  447  X  0-00001986 


Whence  strain =  • 


3-903 


Torque= 

whence/  —  13,510  Ibs.  per  sq.  in. 

0  =  11*87  x  10°  Ibs.  per  sq.  in. 
Now  since  (l  +  er)2C  =  E.'.cr  =  0'298. 


1  Calculated  as  explained  in  ';  Compound  Stress   Experiments,"  Proc.  Inst. 
Mech.  Eng.,  1909. 


250 


APPENDIX  III. 


Stresses  at  Yield-Point. 

_3x2240x4 


X  1-134=9,650  Ibs.  per  sq.  in. 


XI 1005 
p  —  18,110  Ibs.  per  sq.  in. 
.  • .  Maximum  shear  stress  =  18,720. 
Maximum  principal  stress  =  23,540. 
Maximum  principal  strain  =  0'917  x  10-;>1. 


Fraction  of 


Tension 


Yield 


Fra 


Com 


o?    Yfe 


O»  X  o    >.. 


JL  a 


FIG.  130. — Curve  showing  Method  of  Plotting  Results  of  Compound 
Stress  Experiments. 


Mr.  Mason's  Experiments, — At  the  University  of  Liverpool  Mr. 
William  Mason,  M.Sc.,  has  made  experiments  upon  tubes  subjected  to 
compression  and  internal  or  external  fluid  pressure.  An  ingenious 
apparatus  for  holding  the  tubes  in  tension  was  also  designed.  Mr.  Mason 
recognised  the  great  necessity  for,  and  difficulty  of,  obtaining  axial 
loading  in  compression.  There  was  also  very  considerable  trouble  in 
making  reliable  tests  under  simultaneous  axial  and  hoop  compression. 
However,  most  of  these  were  overcome.  The  experiments  recorded  in 


Fracture  of  Cast-iron  Specimens  in  Combined  Torsion  and  Bendin< 


PLATE  IV. 


APPENDIX  III. 


251 


Mr.  Mason's  paper  "  show  an  approximate  agreement  between  the 
maximum  shear-stress  at  the  yield-point  in  compression  and  the  yield- 
point  in  pure  shear,  the  mean  difference  in  the  tests  of  annealed 
specimens  being  about  3  per  cent.  "  Mr.  Mason  concludes  by  saying : 
"It  appears,  then,  that  mild  steel  in  direct  compression  yields  by  shearing  ; 
and  to  a  first  approximation  that  the  value  of  this  shear-stress  is  indepen- 
dent of  any  normal  compressive  stress  on  the  planes  of  the  slide." 

It  is  worth  noting  that  the  Report  of  the  Steel  Committee  of  Civil 
Engineers,  as  far  back  as  1870,  included  results  which  show  very  close 
agreement  between  the  yield-stress  in  tension  and  compression  of  steel 
and  wrought -iron  bars. 

Guest's  Law. — It  is  suggested  that  the  bulk  of  the  evidence  furnished 
by  these  experiments  proves  that  Guest's  law  for  the  failure  of  ductile 
materials  is  accurate  enough  for  design  purposes. 

Brittle  Materials.— Mr.  Walter  Scoble  and  Prof.  Goodman  (of  the 
University  of  Leeds)  have  made  experiments  upon  brittle  materials  such 
as  cast  iron  and  hard  tool  steel.  They  find  that  at  failure  the  maximum 
principal  stress  is  constant.  Fracture  is  the  most  satisfactory  criterion 
of  strength  for  a  brittle  material.  The  table  on  page  252,  from 
Mr.  Scoble's  latest  tests,  supplies  evidence  to  justify  his  conclusions.  It 
is  from  a  paper  recently  (1910)  presented  to  the  Physical  Society. 

Plate  IV.  shows  the  type  of  fractures  obtained. 

Prof.  Goodman  has  made  experiments  and  has  published  the  following 
table,  showing  the  relation  between  the  angle  of  fracture  and  the  principal 
stresses  for  cast-iron  bars  I—- 
TABLE XLIII. 


Twisting 
Moment. 
Lbs.  in. 

Bending 
Moment. 
Lbs.  in. 

Equivalent 
Twisting 
Moment. 

Modulus  of 
Rupture. 
Tons  per 
sq.  in. 

Angle  of  Fracture. 

Actual. 

Calculated. 

Zero 

2,300 

4,600 

25-5 

0° 

0° 

777 

1,925 

4,000 

26-7 

12° 

11° 

1,170 

2,240 

J,750 

27-1 

14° 

14° 

1,228 

2,255 

4,820 

23-1 

17° 

15° 

1,308 

2,128 

4,628 

24-0 

19° 

16° 

2,606 

1,375 

4,320 

20-8 

33° 

31° 

2,644 

766 

3,520 

16-2 

38° 

37° 

3,084 

Zero 

3,084 

16'0 

43° 

45° 

Pure  shear. 

13-0 

0° 

QO  \  Mean  of 

,,     tension. 

11-5 

0° 

()0      numer- 
;  ous  tests. 

COMBINED  STRESS  TESTING  MACHINE. 

A  machine  has  been  erected  at  the  Glasgow  and  West  of  Scotland 
Technical  College  designed  to  give  combined  tests  in  tension  and  torsion. 


252 


APPENDIX  III. 


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APPENDIX  III.  253 

It  will  make  tension  tests  up  to  56,000  Ibs.  and  torsion  test  up  to  12,500 
iuch-lbs.  It  consists  generally  of  an  arrangement  of  levers  and  steel- 
yards by  which  both  the  tests  are  indicated  separately  and  simul- 
taneously, and  an  arrangement  of  worm  and  worm-wheel  gearing  to  give 
the  torsional  test,  the  tension  test  being  applied  by  means  of  a  hydraulic 
cylinder  and  ram.  The  torsion  stress  is  applied  by  hand  power  while 
the  tension  test  is  effected  by  the  use  of  the  town  main  pressure  of  850 
to  1,120  Ibs.  per  sq.  inch. 

The  specimen  is  of  a  maximum  length  between  shoulders  of  30  inches, 
the  largest  diameter  being  1  inch.  The  specimen  may  be  of  the  round 
type,  which  would  be  made  with  square  heads,  or  they  may  be  triangular 
or  rectangular  in  section,  in  which  case  the  specimens  would  not  be  pro- 
vided with  heads.  Either  of  the  foregoing  specimens  can  be  gripped 
between  hardened  steel  wedges  having  serrated  faces.  The  serrations 
secure  the  specimen  from  slipping  during  the  tension  test,  while  the 
tendency  to  rotate  is  resisted  by  a  square  recess  in  the  torsion  shaft  in 
which  the  head  of  the  specimen  fits.  The  recess  is  adapted  to  receive 
various  sections  of  specimens  by  the  insertion  of  packing  dies  having 
recesses  to  suit  the  particular  section  of  specimen.  Three  pairs  of  packing 
dies  are  supplied  with  the  machine. 

The  tension  test  is  applied  by  means  of  a  double-acting  hydraulic 
cylinder  and  ram.  The  cylinder  is  arranged  to  be  worked  by  the  hydraulic 
pressure  from  the  town  mains  at  850  to  1,120  Ibs.  per  sq  inch.  The 
piston  has  a  stroke  of  2  feet  10  inches,  which  allows  2  feet  4  inches  for 
adjustment  for  different  lengths  of  specimens  and  6  inches  more  for  the 
extension  upon  the  maximum  specimen.  The  piston  rod  is  connected  to 
the  tension  shaft  by  means  of  a  swivel  coupling  containing  ball  bearings. 
The  tension  shaft  has  keyed  upon  it  a  worm-wheel,  having  machine-cut 
teeth,  which  is  revolved  by  a  worm-wheel  upon  the  shaft  of  which  a  hand- 
wheel  is  secured.  The  whole  of  the  arrangement  of  worm  gearing  is 
carried  in  a  bracket  which  is  mounted  upon  a  sliding  base.  The  sliding 
base  has  a  machined  underface  and  has  a  groove  which  clips  machined 
guides  upon  the  upper  face  of  the  bed. 

The  torsion  test  is  applied  by  means  of  a  worm  and  worm-wheel.  The 
worm-wheel  revolves  in  ball-bearings  to  reduce  the  friction  caused  by  the 
tension  test. 

The  specimen  takes  up  the  torque  by  means  of  a  square  shaft 
sliding  in  a  sleeve,  upon  which  the  main  torsion  lever  is  keyed. 
This  shaft  is  allowed  to  move  slightly  in  a  longitudinal  direction  by  an 
arrangement  of  hardened  steel  rollers.  These  rollers  bear  against  rect- 
angular projections  upon  the  shaft,  and  while  allowing  the  longitudinal 
movement  due  to  the  tension  test  to  take  place,  at  the  same  time  resist 
the  tendency  of  the  shaft  to  rotate  inside  the  sleeve. 

The  sleeve  of  the  torsion  shaft  is  mounted  upon  ball-bearings  which  run 
in  hardened  steel  races  carried  by  a  short  cast-iron  column  which  is 
bolted  down  to  the  bed. 


254  APPENDIX  III. 

The  sleeve  is  connected  by  means  of  a  ball-bearing  muff  to  the  main 
link  which  communicates  the  tension  stress  to  the  main  lever  for  the 
tension  test.  Any  rotary  tendency  upon  the  part  of  the  muff  is  resisted 
by  means  of  check  links.  The  hand-wheels  for  propelling  the  poises  for 
the  two  steelyards  are  placed  close  together  so  as  to  be  worked  by  one  man. 
The  two  steelyards  are  so  placed  that  neither  interferes  with  the  readings 
upon  the  other.  The  details  of  this  machine  were  supplied  by  the  makers 
(Messrs.  Avery),  from  whom,  doubtless,  more  details  can  be  obtained. 


PIG.  131. — Diagram  to  show  Method  of  Loading  in  a  Combined  Bending 
and  Torsion  Test  on  Dr.  Coker's  Apparatus. 

So  far  as  the  author  is  aware  no  actual  results  on  combined  stress  carried 
out  on  this  machine  have  been  published. 

The  details  of  an  arrangement  for  making  combined  stress  tests  with 
the  ordinary  vertical  testing  machine,  used  with  some  success  at  the  East 
London  College  (Fig.  129),  are  simple  and  easily  made. 

A  Combined  Torsion  and  Bending  Machine. — Prof.  E.  G.  Coker 
has  designed  an  apparatus  by  which  tests  can  be  performed  in  combined 
bending  and  torsion.  The  principle  on  which  the  design  is  based  is  illus- 
trated by  Fig.  131,  in  which  the  rod  R  is  suspended  at  intermediate  points 
A,  B,  by  wires  C,  D,  depending  from  a  fixed  support  E.  The  equal  over- 
hanging ends  of  the  rod  are  loaded  by  weights  W,  so  that  the  applied 
couple  between  the  points  of  support  is  uniform  and  of  amount  Wa,  where 
a  is  the  length  of  the  lever-arm.  The  rod  is  also  twisted  by  weights  "Wi 


APPENDIX  III.  255 

attached  to  equal  arms  of  length  b,  so  that  there  is  a  uniform  twisting 
moment  of  amount  Wi&  between  the  points  of  suspension.  The  two  systems 
of  loading  are  independent,  and  their  ratio  can  be  adjusted  to  any  value 
desired. 

In  carrying  out  this  arrangement  in  practice  it  is  convenient  to  arrange 
that  one  of  the  levers  for  applying  the  twisting  moment  shall  always 
remain  in  a  horizontal  position,  and  that  the  other  shall  be  capable  of 
turning  through  an  arc  to  bring  the  first  lever  back  to  zero  after  each 
application  of  the  load.  The  most  convenient  way  of  carrying  this  out  is 
to  replace  the  adjustable  lever  by  a  worm  and  worm-wheel  gear  secured 
in  a  casing  and  turned  by  a  hand-wheel  (see  Fig.  132).  To  allow  freedom 
for  bending,  the  worm-wheel  casing  must  be  pivoted  to  rotate  around  a 
line  intersecting  the  axis  of  the  specimen  and  perpendicular  thereto,  and 
this  method  of  pivoting  must  also  be  adopted  at  the  horizontal  lever. 
This  arrangement  only  differs  from  that  of  the  perfectly  freely  suspended 
arrangement  shown  in  Fig.  131  in  fixing  one  point  of  the  rod,  and  this 
has  the  indirect  advantage  of  stilling  vibration,  which  is  troublesome  in 
the  freely  suspended  bar. 

The  various  parts  are  supported  in  a  built  up  frame  consisting  of  two 
planished  steel  shafts  A  secured  in  cast-iron  cross  frames  B  mounted  on 
four  standards,  one  of  which  latter  is  adjustable  in  height  to  secure 
steadiness  on  an  uneven  floor.  Upon  the  steel  shafts  are  two  castings  C, 
D,  each  of  which  has  a  cylindrical  bearing  E  encircling  one  of  the  shafts 
and  resting  with  a  flat  face  F  in  line  contact  with  the  other  shaft,  and 
secured  in  position  by  a  cross-bar  G  threaded  on  studs.  This  connection 
is  perfectly  rigid,  since  it  removes  all  degrees  of  freedom  and  it  is  readily 
released  by  simply  turning  back  one  of  the  cross-bar  nuts,  leaving  the 
casting  free  to  slide  into  a  new  position.  It  also  has  the  advantage  that 
no  accurate  fitting  is  required  for  the  supporting  frame.  The  casting  C, 
carrying  the  worm-wheel  gear  W  has  trunnion  bearings  H  at  right  angles 
and  to  intersecting  the  axis  of  the  specimen.  The  bearings  are  fitted 
with  friction  rollers,  and  when  the  machine  is  used  simply  for  torsion  the 
worm-wheel  is  kept  in  a  vertical  position  by  an  arm  I  keyed  to  the  bearing 
H  and  locked  in  position  by  a  thumb-screw.  A  weight  J  attached  by  an 
arm  to  the  second  bearing  balances  the  pivoted  casing  in  all  positions. 

The  weight  levers  are  supported  from  a  vertical  standard  K  of  the 
frame  D  by  a  wire  L,  terminating  in  a  thin  plate  M  with  a  keyhole  slot 
encircling  the  spindle  N.  Formerly  a  roller  bearing  was  used  for  this 
spindle,  but  this  is  an  unnecessary  refinement  as  the  friction  is  extremely 
small,  and  can  be  easily  taken  into  account.  The  casting  supported  in 
this  way  has  three  levers,  P,  Q,  and  E,  the  first  two  of  which  are  for  the 
application  of  twisting  moments,  and  the  third  E,  in  the  line  of  the 
specimen,  is  for  applying  a  bending  moment. 

All  the  loading  levers  are  provided  with  knife-edges,  of  circular 
form,  made  by  turning  an  ordinary  Whit  worth  nut  down  to  form  a 
disc  with  a  Y-shaped  edge.  These  discs  carry  rings  T  with  wide-angled 


APPENDIX  III. 


APPENDIX  III. 


257 


V-shaped  recesses  on  the  inner  sides,  and  light  rods  U  screwed  into  these 
rings  carry  the  weight.  This  arrrangement  of  knife-edge  is  very  easy  to 
adjust  accurately,  and  when  bending  and  twisting  stress  are  applied 
simultaneously  the  rolling  line  contact  adjusts  itself  to  the  bending  and 
twisting  of  the  specimen.  The  bending  of  the  specimen  causes  a  change  in 
the  effective  arm  of  the  bending  levers,  which  is  generally  negligible,  but  a 
correction  may  be  necessary  with  a  very  long  specimen.  For  if  a  is  the 
length  of  the  lever  arm  and  b  is  the  radius  of  the  circular  knife-edge,  an 
angular  deviation  of  amount  0  will  cause  a  change  of  a— (a  cos  0  -f-  6  sin 
0)  in  the  lever-arm,  and  this  is  zero  when  0  =  0,  and  also  when  a  =  a 
cos  e  -f-  b  sin  0.  In  one  machine  built  to  this  design  the  correction  curve 
came  out  as  given  in  Fig.  133.  In  the  majority  of  tests  the  angular 


S+l 


o 


10° 


FIG. 


2°  4°  6°  8° 

Angle  of  Bending 

133. — Curve  of  Correction  Factor  for  Professor  Coker's  Combined 
Bending  and  Torsion  Machine. 


change  at  the  ends  rarely  exceeds  5°,  and  the  correction  is  therefore  so 
very  small  as  to  be  practically  negligible. 

The  worm-wheel  W  and  the  casting  V  for  the  weight-levers  are  bored 
out  to  receive  the  ends  of  the  specimen,  and  are  provided  with  fixed  keys 
which  slide  in  corresponding  key- ways  cut  in  the  specimen.  When  tubes 
are  subjected  to  stress  they  are  provided  with  solid  ends  secured  by 
transverse  pins,  thereby  avoiding  brased  joints,  since  these  latter  are 
troublesome,  owing  to  the  state  of  the  metal  being  altered  by  the  brasing. 
The  end  of  the  specimen  projecting  through  the  worm-wheel  is  fitted 
with  a  lever  X  for  applying  bending  moment,  and  both  levers  for  bending 
may  be  loaded  independently  or  by  a  cross-bar  suspended  from  stirrups 
as  shown  in  Fig.  132. 

Fig.  132  shows  three  views  of  a  machine  built  on  the  principle  here 
described.  The  actual  machine  shown  is  one  built  by  students  of  the 
City  and  Guilds  Technical  College,  Finsbury. 

T.M.  S 


258 


APPENDIX  III. 


Prof.  E.  G.  Coker's  Instrument  for  Measuring  Torsion  and 
Bending  Strains. — This  instrument  was  originally  designed  to  measure 
the  angle  of  twist  within  the  elastic  limit,  but  the  design  shown  can  be 
adjusted  in  a  few  seconds  for  measuring  the  angular  change  due  to 
bending.  The  calibration  of  the  readings  is  effected  on  the  specimen 
and  serves  for  both  bending  and  twisting.  Fig.  134  shows  the  apparatus 
in  part  longitudinal  section. 

It  consists  of  a  graduated  circle  A  mounted  on  the  specimen  B  by 
three  screws  C  in  the  chuck-plate  D.  A  sleeve  E  provided  with  three 
screws  grips  the  specimen  at  a  fixed  distance  away  from  the  first  set. 

The  spacing  of  these  two  main  pieces  on  the  specimen  is  effected  by  a 


Rack 


alance  Weight 


FIG.    134. — Professor   Coker's    Torsiometer  for  Measuring  Strains  in  a 
Combined  Bending  and  Torsion  Test. 

clamp,  not  shown  in  the  figure,  which  grips  the  double  cones  F,  G,  and 
maintains  them  at  the  correct  distance  apart,  until  the  set  screws  are 
adjusted. 

The  clamp  is  afterwards  removed,  leaving  the  plane  of  the  graduated 
circle  perpendicular  to  the  axis  of  the  specimen  and  the  sleeve  correctly 
set  and  ready  to  receive  the  reading- microscope  H. 

The  vernier  plate  carries  a  sliding  tube  I,  on  which  a  wire  J  is  mounted, 
and  the  movement  of  this  latter  due  to  bending  or  twist  is  measured  by  a 
scale  in  the  eye-piece  K,  the  divisions  of  which  are  calibrated  by  reference 
to  the  graduated  circle.  It  is  found  convenient  to  have  the  microscope - 
tube  pivoted  about  an  axis  perpendicular  to  its  central  line  at  L,  so 
that  any  slight  difference  due  to  imperfect  centering  can  be  adjusted 
by  the  screw  M  to  make  the  calibration  value  agree  for  a  series  of 
specimens. 


APPENDIX  III.  259 

The  observation  wire  may  be  set  at  any  convenient  position  for  calibra- 
tion, but  for  observations  of  the  angle  of  twist  when  the  specimen  is  also 
subjected  to  a  uniform  bending  moment  the  wire  should  be  in  the  central 
plane  perpendicular  to  the  specimen.  For  if  the  bending  is  in  the  plane 
containing  the  axis  of  the  specimen  and  the  observation  wire,  it  has  the 
effect  of  causing  new  parts  of  the  wire  to  come  into  vi^w  on  the  scale,- 
but  110  error  is  caused  thereby.  If  the  specimen  is  bent  in  a  plane  at 
right  angles  to  the  former,  then  the  change  in  the  reading  is  (0—<f>}l, 
where  6  and  ^  are  the  alterations  of  angle  at  the  ends  and  11  is  the  length 
of  the  specimen  under  observation.  Since  the  bending  is  uniform  8  —  <$>  and 
no  correction  is  necessary.  Bending  in  any  other  plane  can  be  resolved 
into  components  in  the  vertical  and  horizontal  planes,  and  therefore  falls 
under  the  preceding  cases.  In  order  to  effect  the  adjustment  required, 
both  the  wire  and  the  microscope  slide  in  adjustable  tubes  provided  with 
graduated  scales,  and  the  movement  to  bring  the  wire  into  focus,  is 
divided  between  them.  To  check  the  setting  of  the  wire  in  the  central 
position  it  is  convenient  to  apply  a  uniform  bending  moment,  and  then 
to  observe  if  any  change  takes  place  in  the  reading.  The  position  for  no 
change  in  the  reading  can  be  found  in  a  few  seconds. 

In  experiments  where  the  bending  moment  is  constant  and  the  twisting 
moment  is  varied,  no  adjustment  is  practically  required  during  the  elastic 
life  of  the  specimen ;  and  even  when  the  bending  moment  is  variable  the 
adjustment  is  practically  negligible,  as  the  length  of  the  specimen  under 
test  is  only  a  few  inches. 

The  instrument  is  used  for  observations  of  the  angular  change  due  to 
bending  by  adjusting  the  wire  in  the  horizontal  plane  passing  through 
the  axis  of  the  specimen,  and  at  a  fixed' distance  away  from  the  central 
plane,  as  shown  in  Fig.  134.  Thus  if  the  wire  is  at  a  distance  x  from  the 
central  plane,  and  the  specimen  is  subjected  to  a  uniform  bending 
moment,  the  reading  will  be  (l+x)  Q—(l—x}  0=2x6,  and  this  is  a  measure 
of  the  angular  change  0  between  the  ends,  since  any  further  corrections 
are  negligible  for  elastic  strains. 

The  instrument  may  therefore  be  used  for  measuring  strains  due  to 
bending  or  twisting,  and  the  single  calibration  required  for  both  sets 
of  readings  is  effected  when  the  instrument  is  in  position  on  the 
specimen. 

Further  Researches. — Although  the  laws  for  the  failure  of  mild  steel 
and  very  brittle  materials  (cast  iron  and  hardened  tool  steel)  are  now 
established,  it  yet  remains  to  be  shown  whether  other  materials  fail  by 
these  laws.  The  effect  of  repeated  stress  upon  ductile  materials,  and  its 
bearing  upon  failure  under  combined  stress,  also  requires  investigation. 
Th€;re  are  numerous  original  experiments  for  those  having  the  requisite 
facilities. 


s  2 


APPENDIX    IV. 


HEAT  TREATMENT  OF  STEELS. 

IT  is  impossible,  in  this  book,  to  give  a  full  account  of  the  work  done  on 
heat  treatment  of  various  steels.  However,  Prof.  A.  McWilliam  and  Mr. 
E.  J.  Barnes,  of  the  University  of  Sheffield,  have  recently  published1  a 
very  complete  study  of  the  effect  of  heat  treatment  on  Bessemer  steels,  and 
the  following  facts,  abstracted  from  their  paper,  will  serve  as  a  guide  for 
work,  either  upon  similar  material  or  some  other  types  of  steel.  The  tests 
were  made  on  ordinary  commercial  English  acid  Bessemer  steels  of 
carbon  content  varying  from  O'lO  per  cent,  to  0'86  per  cent.  The 
steels  were  received  and  treated  in  the  form  of  forged  or  rolled  bars  1  inch 
round,  and  either  as  received  or  after  the  treatment  detailed  were  all 
tested  in  tensile,  and  as  far  as  possible  also  under  Dr.  Arnold's  alternating 
stress  test,  and  were  examined  under  the  microscope. 

Treatments  with  Distinguishing  Letters. 

Treatment.  Letter. 

As  received B 

Normalised.     950°  0.  for  20  minutes  and  cooled  in  air     .  BN  . 
Annealed.     Slowly  heated  up  to  950°  C.  ;  kept  at  950°  C. 

for  about  35  hours ;  very  slowly  cooled  down  in  furnace  BA  - 

Quenched  from  850°  C.  in  water  and  tempered  at  400°  C.  BY 

500°  C.  BX 

600°  C.  BZ 

700°  C.  BW  " 

,,     900°  C.     ,,  „  ,,  600°  C.  BJ" 

700°  C.  BK  - 

,,     950°  C.     „  „  „          700°  C.  BH 

Some  typical  curves  of  this  series  were  given  in  Fig.  68,  page  105. 

Methods  of  Experiment. — All  steels  were  in  the  form  of  1-inch 
round  bars,  and  were  sawn  into  lengths  of  about  11  inches.  Some  of  the 
harder  steels  showed  a  peculiar  structure  after  being  sawn  off,  the  sawn 
surface  exhibiting  a  curious  pattern  of  intersecting  elliptical  elevations 
about  £  inch  broad.  These  gave  no  indications  of  their  presence  in  the 
polished  and  etched  micro -sections. 

1  Iron  and  Steel  Institute,  May,  1909. 


APPENDIX  IV.  261 

Normalising. — The  pieces  were  placed  in  a  Fletcher  gas  muffle  at 
about  750°  C.,  slowly  raised  in  about  half-an-hour  to  950°  0.,  and  so 
maintained  for  twenty  minutes.  They  were  then  taken  out,  reared  on 
end  on  firebricks,  and  allowed  to  cool  in  the  air. 

Annealing. — Annealing  was  carried  out  in  a  coal-fired  reverberatory 
furnace,  according  to  the  details  described  in  the  general  table  of 
treatments. 

Quenching. — The  bars  were  heated  in  a  Brayshaw  salt  bath  furnace, 
the  temperature  of  which  was  simultaneously  determined  by  a  platinum 
resistance  pyrometer  with  Whipple  recorder  and  by  a  Paul  Pt.  —  Pt. —  10 
per  cent.  Ir.  thermo-couple,  the  latter  calibrated  by  means  of  sulphur 
(444°  C.)  and  silver  (962°  0.).  When  the  temperature  was  kept  steady 
these  two  pyrometers  were  in  remarkably  close  agreement,  but,  as  was  to 
be  expected,  on  a  falling  temperature  the  readings  of  the  former  were 
somewhat  higher,  and  on  a  rising  temperature  a  similar  amount  lower 
than  those  of  the  latter.  The  pieces  were  put  in  the  bath  when  it  had 
attained  a  temperature  of  about  50°  C.  lower  than  the  quenching  tempera- 
ture desired;  the  heat  was  gradually  raised  to  the  temperature  and 
maintained  for  fifteen  minutes,  when  they  were  rapidly  withdrawn  and 
instantly  quenched  in  pure  Sheffield  water  at  15°  to  20°  C.  The  molten 
salts  entirely  prevented  scaling,  and  thus  the  quenching  was  as  efficient 
as  the  temperature  used,  compared  with  the  size  of  the  bars,  would  admit. 

As  much  that  is  misleading  has  been  published  on  hardening,  the 
subject  is  considered  shortly  here  as  it  is  involved  in  the  reasons 
for  choosing  a  hardening  temperature  of  850°  C.  for  the  majority 
of  their  quenchings.  In  ordinary  hardening  it  is  essential  that 
the  piece  of  steel  should  be  heated  to  a  temperature  such  that  when 
quenched  it  will  throw  off  its  scale,  or  "  shale  "  as  the  hardener  calls  it.  Tf 
any  of  this  scale  remains  firmly  adhering,  whether  from  the  nature  of  the 
steel  or  the  temperature  used,  then  it  acts  as  a  blanket  over  the  part  of 
the  steel  it  covers,  prevents  efficient  quenching,  and  the  part  underneath 
this  scale  will  be  soft.  A  hardening  temperature  which  results  in  the 
steel  properly  shaling  is  also  in  general  a  temperature  that  will  give 
efficient  quenching  ;  but  when  steels  are  heated,  as  in  a  salt  bath,  so  that 
no  scaling  takes  place,  an  efficient  quenching  temperature  seems  to  be  a 
function  of  the  dimensions  of  the  cross-section  of  the  steel,  for  steels  of 
the  same  composition  and  previous  treatment.  Even  when  bars  were  put 
into  the  salt  bath  with  the  original  rolling-mill  scale  on  them  the  molten 
salt  seemed  to  remove  it  during  the  heating  process. 

Experience  with  hardening  steels  of  various  sections  led  the  authors  to 
consider  800°  to  850°  C.  a  suitable  range,  and  as  some  of  their  steels  were 
very  mild  they  decided  on  the  higher  limit,  850°  C.,  for  their  preliminary 
series  of  tests.  This  was  fixed  only  in  consultation  on  hardening  work 
done,  and  not  from  the  study  of  the  previous  work  of  others  which  had 
been  read  as  it  came  out.  The  previous  work  was  re-read  only 
immediately  before  writing  the  paper,  so  the  coincidence,  of  the 


262  APPENDIX  IV. 

choice  of  850°  C.  with  the  opinions  of  such  a  vigorous  and  reliable  worker 
as  Wahlberg  after  reviewing  his  own  elaborate  series,  done  from  an 
entirely  different  standpoint,  is  of  great  interest. 

Tempering. — With  one  exception  the  tempering  was  done  by  putting 
the  bars  in  a  lead  bath  at  the  required  temperature,  and  maintaining  the 
bath  at  a  constant  temperature  for  fifteen  minutes,  when  the  bars  were 
removed  and  cooled  in  the  air.  In  carrying  out  this  treatment  it  is 
necessary  to  remember  that  samples  of  steel  float  in  molten  lead  like 
wood  in  water,  and  that  some  efficient  means  must  be  adopted  for 
pressing  them  down  into  the  liquid  lead.  The  tray  of  the  Brayshaw 
furnace  weighted  with  a  billet  on  the  top  part  of  the  frame  outside  the 
bath  was  used  with  success.  The  exception  mentioned  above  arose  as 
follows : — 

It  was  desired  to  save  the  trouble  of  holding  the  pieces  down  in  the 
bath  whenever  possible,  and  hence  as  the  Brayshaw  mixture  of  one 
molecular  weight  of  potassium  chloride  (74'5)  to  one  molecular  weight  of 
sodium  chloride  (58'5),  or  in  the  proportion  of  about  2|  Ibs.  to  2  Ibs., 
melts  at  about  650°  C.,  it  was  thought  that  the  tempering  at  700°  could 
be  easily  done  in  this  bath.  He  who  taketh  short  cuts  seeketh  trouble. 
The  bath  was  steadied  at  the  exact  temperature,  and  the  pieces  put  in 
and  kept  fifteen  minutes  at  700°  C.,  but  on  endeavouring  to  get  them 
out  it  was  found  that  with  the  whole  furnace  cooling,  the  top  had  become 
pasty,  and  ultimately  set  before  they  could  be  removed  ;  so  that  it  was 
necessary  to  put  on  a  little  more  gas,  and,  after  re-melting  the  bath, 
keep  agitating  the  whole  right  up  to  the  top  and  thus  get  the  bars 
removed.  The  total  operation  took  forty-five  minutes,  during  which  the 
pieces  had  been  down  to  about  600°  C.  and  then  up  again  to  700°  0. 
Unless  the  recently  described  potassium  bichromate  and  potassium 
chloride  mixture,  which  melts  at  360°  C.,  proves  to  be  non-oxidising  to 
steel  immersed  in  it,  the  authors  are  likely  to  use  a  metallic  bath  only 
for  future  temperings. 

The  tensile  test-pieces  were  all  turned  to  0'564  diameter  and  2  inches 
parallel,  and  the  tensile  piece  was  turned  as  near  as  possible  to  one  end, 
so  that  after  fracture  the  other  end  was  long  enough  to  turn  to  the 
standard  alternating  stress  test-piece,  namely  f  inch  diameter  by  6  inches 
long.  The  micro-sections  were  cut  off  the  unstrained  part,  of  the  short 
end  of  the  tensile  test-piece.  Thus  the  alternating  stress  tests  and  micro- 
sections  were  not  off  duplicate  bars  put  through  the  same  series  of 
operations,  but  by  the  methods  adopted  represent  tests  actually  off  the 
same  piece. 

The  composition  of  one  of  the  steels1  with  regard  to  carbon  and 
manganese  is  given  on  page  263,  the  carbon  being  determined  by  com- 
bustion and  checked. 

1  The  original  paper  contains  records  of  several  steels,  but  one  type  only  is 
given  here, 


APPENDIX  IV. 


263 


TABLE  XLV.— SHOWING  EFFECT  OF  HEAT  TREATMENT  ON  STEEL  OF 
CARBON  0*10  PER  CENT.  AND  MANGANESE  0*56  PER  CENT. 


Treatment. 

Mark. 

Yield 
Point. 
Tons  per 
sq.  in. 

Maximum 
Stress. 
Tons  per 
sq.  in. 

Elonga- 
tion.   Per 
cent,  on 
2  in. 

Reduction 
of  Area. 
Per  cent. 

Dr. 

Arnold's 
Alternating 

Stress  Test. 

As  received 

10  B 

19-1 

25-9 

37-1 

63-4 

— 

Normalised 

10  BN 

18-5 

24-8 

37-4 

59-8 

— 

Annealed  . 

10  BA 

9-6 

21-0 

43-8 

72-0 

352 

850°     C.     water 
and  400°  C.  air 

10  BY 

17-9 

27  4 

39-0 

72-9 

— 

850°     C.    water 
and  500°  C.  air 

10  BX 

17-6 

26-0 

38-0 

74-7 

336 

850°    C.     water 
and  600°  C.  air 

10  BZ 

19-4 

26-0 

38-5 

71-6 

326 

850°     C.    water 
and  700°  C.  air 

10  BW 

16-7 

26-1 

40-0 

74-5 

331 

950°    C.     water 
and  700°  C.  air 

10  BH 

21-1 

28-4 

35-0 

67-5 

239 

TABLE  XL VI. — THE  EFFECT  OF  HEAT  TREATMENT  ON  STEEL  OF  CARBON 

0'29   PER   CENT.   AND   MANGANESE   0'92   PER   CENT. 


Mark. 

Yield  Point. 
Tons  per 
sq.  in. 

Maximum 
Stress. 
Tons  per 
sq.  in. 

Elongation 
per  cent, 
on  2  in. 

Reduction  of 
Area  per 
cent. 

Dr.  Arnold's 
Alternating 
Stress  Test. 

30  B 

26-6 

40-9 

25-0 

46-8 

322 

30  BN 

25-7 

40-8 

26-3 

63*5 

329 

30  BA 

21-5 

37-1 

26-5 

4S-C 

296 

30  BW 

37*0 

45-7 

25'j 

o7'8 

202 

30  BJ 

50-9 

57'5 

17-3 

48-6 

173 

30  BK 

46-2 

54-3 

19-5 

50-8 

184 

The  table  containing  the  30  B  results  shows  the  very  marked  influence 
of  the  higher  quenching  temperatures,  namely,  900°  for  30  BJ  and  30  BK, 
even  after  these  have  been  tempered  at  600°  and  700°  respectively ;  for 
example,  the  high  reduction  in  area,  51  per  cent.,  for  a  54-ton  steel  with 
yield  point  85  per  cent,  of  the  maximum  stress. 


264 


APPENDIX  IV. 


As  showing  the  effect  of  heat  treatment  on  other  than  Bessemer  steels 
the  following  table  from  a  paper  on  "High  Tension  Steels," l  by  Mr. 
Percy  Longmuir,  B.Met.,  read  before  the  Iron  and  Steel  Institute,  is 
instructive  : — 

TABLE  XLVII. — 5  PER  CENT.  XICKEL  STEEL. 


No. 

Treatment. 

Elastic 
Limit. 
Tons  per 
sq.  in. 

Maximum 

Stress. 
Tons  per 
sq.  in. 

Elongation 
per  cent, 
on  2  in. 

Reduction 
of  Area 
per  cent. 

23 

As  received  .... 

47-6 

56«96 

13-5 

20-0 

24 

Air  cooled  from  800°  C. 

34-8 

49-08 

18-0 

38-0 

2o 

Heated  to  1  ,000°  0.,  quenched 

in   oil  at    1,000°  C.,  tem- 

j 

pered  at  490°     . 

04-8 

76-00 

12-5 

43-6 

20 

Heated  to  1,  000°  C.,  quenched 

in  oil  at  1,000°  C.,  tem- 

pered at  490°      . 

68-4          70-92 

10-0 

37-6 

27 

Heated  to  1,  000°  C.,  quenched 

in  oil  at  900°  C.,  tempered 

at  490°       .... 

66'8 

70-08 

12  'a 

4,3-2 

28 

Heated  to  1,  000°  C.,  quenched 

Not 

in  oil  at  9o()°  C.,  tempered 

de- 

at 490°       .... 

tected 

82-56 

1-.3 

0-4 

29 

Heated  to  800°  C.,  quenched 

in  oil  at  800°  C.,  tempered 

at  490°       . 

05-2 

78-40 

3-0 

2-5 

The  above  results  will  probably  inspire  the  reader  to  conduct  similar 
tests  under  various  conditions.  The  authors  of  the  above  paper  do  not 
give  details  concerning  the  method  of  gripping  the  specimens,  etc.,  and  it 
is  therefore  not  possible  to  estimate  within  what  measure  of  accuracy 
some  of  the  jigures  come.  That  they  form  a  valuable  guide  and  refer- 
ence cannot  be  doubted.  The  enormous  amount  of  work  entailed  in  such 
a  research  can  only  be  appreciate  1  by  those  who  have  attempted  similar 
experiments. 

Captain  H.  B.  Sankey  and  Mr.  J.  Kent-Smith  published  a  paper'2 
entitled  "  Heat  Treatment  Experiments  with  Chrome-Vanadium  Steel." 
The  reader  who  wishes  to  do  original  work  on  this  subject  would  do  well 
to  consult  the  journals  of  the  scientific  institutions  or  the  pages  of 
"Science  Abstracts"  for  the  last  ten  years.  At  the  same  time  there  is 
no  need  for  the  student  who  seeks  to  do  new  laboratory  experiments  to 
hesitate  because  someone  else  has  done  the  same  thing. 


1  Proceedings,  Iron  and  Steel  Institute,  May,  1909. 

2  Transactions  of  the  Institution  of  Mechanical  Engineers,  1904. 


BIBLIOGRAPHY. 


APPLIED  MECHANICS  TEXT  BOOKS  CONTAINING  GENEEAL 
EEFEEENCES  TO  THE  STRENGTH  OF  MATERIALS  AND 
TESTING. 

Applied  Mechanics.     EANKINE.     (Griffin,  London.) 

Applied  Mechanics.     COTTERILL.     (Macmillan,  London.) 

Mechanics  of  Engineering.     CHURCH.     (Wiley,  New  York.) 

Mechanics  Applied  to  Engineering.     GOODMAN.     (Longmans,  London.) 

Applied  Mechanics.     LANZA.     (Wiley,  New  York.) 

Applied  Mechanics.    ALEXANDER  and  THOMPSON.  (Macmillan,  London.) 

Applied  Mechanics.     PERRY.     (Cassell,  London.) 

Applied  Mechanics  and  Mechanical  Engineering  (five  vols.).     JAMIESON. 

(Griffin,  London.) 

Mechanical  Engineering.     CARPENTER.     (Wiley,  New  York.) 
Experimental  Mechanics.     BALL.     (Macmillan,  London.) 
Applied  Mechanics.     D.  A.  Low.     (Longmans,  Green  &  Co.,  London.) 
Experimental  Engineering.      E.   C.  CARPENTER.      (Chapman  &  Hall. 

1905.) 
Theory  of  Structures  and  Strength  of  Materials.     II.  T.  BOVEY.     (John 

Wiley  &  Sons,  New  York.) 
Chain  Cables  and   Chains.      THOS.  W.  TRAILL,  M.Inst.C.E.      (Crosby, 

Lockwood  &  Co.) 

Strength  and  Properties  of  Materials.     (W.  G.  Kirkcaldy,  London.) 
Mechanical    Engineering   Materials.      E.    C.    E.    MARKS.      (Technical 

Publishing  Co.) 
Strength  of  Materials  and  Structures.     SLR  J.  ANDERSON.     (Longmans, 

Green  &  Co.,  1892.) 

Design  of  Structures.     S.  ANGLIN.     (Chas.  Griffin  &  Co.) 
Bridge  Construction.     PROF.  FIDLER,  M.E.C.E.     (Chas.  Griffin  &  Co.) 
Testing  Materials  (two  vols.).     MARTENS  and  HENNING.      (Wiley,  New 

York.) 

Mechanics  of  Materials.     MERRIMAN.     (Wiley,  New  York.) 
Theory  of  Structures  and  Strength  of  Materials.     BOVEY.     (Wiley,  New 

York.) 

Testing  of  Materials.     UNWIN.     (Longmans,  London.) 
The  Strength  of  Materials.     EWING.     (Cambridge  University  Press.) 
Strength  of  Materials.     MORLEY.     (Longmans,  London.) 
Elasticity  and  Eesistance  of  Materials.     BURR.     (Wiley,  New  York.) 


266  BIBLIOGEAPHY 

Materials  of  Construction.     JOHNSON.     (Wiley,  New  York.) 

Materials  of  Engineering  (three  vols.)     THURSTON.     (Wiley,  New  York.) 

A  History  of  the  Theory  of  Elasticity  and  of  the  Strength  of  Materials. 

TODHUNTER  and  PEARSON.     (Cambridge  University  Press.) 
Strength  and  Elasticity  of    Structural   Members.      WOODS.      (Arnold, 

London.) 
Testing  and  Strength  of  Materials.     POPPLEWELL.    (Scientific  Publishing 

Co.,  Manchester.) 

MISCELLANEOUS     PAPERS,    ETC.,    ON    TESTING,  AND    SUB- 
JECTS   CONNECTED    WITH    TESTING. 

Naval    Accidents    (Microstructure,    &c.).       THOS.    ANDREWS,    F.B.S. 

(Engineering,  Dec.  2nd,  1904,  pp.  737  et.  seq.} 
The  Adoption  of  Standard  Forms  of  Test-Pieces  for  Bars  and  Plates, 

by  WILLIAM  HACKNEY,  B.Sc.,  Assoc.M.Inst.C.E.    (Proc.  Inst.  C.  E., 

vol.  Ixxvi.,  part  ii.) 
The  Shape  of  Compression  Test-Pieces.    A.  MARTENS.  (Ibid.,  vol.  cxxvii., 

p.  400.) 
Forms  of  Tensile  Test-Pieces.     S.  L.  H.  APPLEBY.     (Ibid.,  vol.  cxviii., 

p.  395.) 
The    Practical    Strength    of    Beams.       (Proc.    Inst.    C.  E.,    vol.    Ixii., 

p.  251.) 
Tensile  Tests  of  Iron  and  Steel  Bars.    PETER  D.  BENNETT.     (Prcc. 

Inst.  M.  E.,  1886.) 
Testing  Some  Specimens  of   Malleable  Cast  Iron.      A.    G.   ASHCROFT. 

(Proc.  Inst,  C.  E.,  vol.  cxvii.,  1894.) 
The  Resistance  of  Materials  under  Impact.      MANSFIELD  MERRIMAN. 

(Ibid.,  vol.  cxxii.,  1895.) 
A  New  Indentation  Test  for  Determining  the  Hardness  of  Metals,  by 

W.  C.  UNWIN,  B.Sc.,  F.R.S.     (Ibid.,  vol.  cxxix.,  1897.) 
Testing  the  Strength  of  Materials.     A.  H.  JAMESON,   M.Sc.     (Ibid.,  vol. 

cxxxiv.,  1898.) 
Notes  on  the  Endurance    of    Steel    Bars     Subject  to    Repetitions   of 

Torsional  Tests,  by  E.  G.  COKER,  B.A.,  B.Sc.     (Ibid.,  vol.  cxxxv., 

1899.) 
The  Relation  of  the  Constants  of  the  Elongation  Equation  to  Contraction 

of  Area.     PROF.  ELLIOTT.    (Ibid.,  vol.  clviii.,  1904.) 
The  Fatigue  of  Metals.     A.  N.  KEMP.     (Engineering  Review,  1904.) 
A   Throw -testing    Machine   for   Reversals   of  Mean  Stress,    by    Profs. 

OSBORNE  REYNOLDS,  F.R.S. ,  and  J.  H.  SMITH,  M.Sc.,  etc.    (Phil. 

Trans,  of  the  Roy.  Soc.  of  London,  vol.  199,  1902.) 
Heat     Treatment    Experiments     with     Chrome-Vanadium     Steel,     by 

CAPT.  H.  R.  SANKEY  and  Mr.  J.  K.  SMITH. 
Wohler's    Experiments    and     Results.     ("  Zeitschrift    fur    Bauwesen,"< 

Berlin,  1870  ;  and  Engineering,  vol.  ix.,  1871.) 


BIBLIOGEAPHY  267 

Fatigue  of  Materials.     A.  N.  KEMP.     (Engineering  Revieiv,  Sept.,  1904.) 
Launhardt's  Experiments.    ("  Zeitschrift  des  Architecten  und  Ingenieur- 

Yereins,"  Hanover,  1873.) 
Further     Wohler    Experiments.       SPANGENBERG.      ("  Zeitschrift     fiir 

Bauwesen,"  1874.) 
Experiments  on  Iron  and  Steel  (Alternating  Stresses).     SIR  BENJAMIN 

BAKER,  M.Inst.O.E.     (American  Soc.  Mech.  Engineers,  1886.) 

•  Variation  of  the  Elastic  Limits  of  Materials.      BAUSCHINGER.     (Mitt- 

heilungen  aus  dem  Mech.  Techn.  Laboratorium  in  Munchen,  1886.) 
Fracture  of  Metals  under  repeated  Alternations  of   Stresses.      PROF. 
EWING  and  J.  C.  W.  HUMPHREY.     (Eoy.  Soc.,  1903.) 

•  Der  Einfluss  von  Ungleichmassigkeiten  in  Querschnitte  des  prismatischen 

Theiles  eines  Probestabes.  ("  Zeitsch.  Yer.  Deutsch.  Ing.,"  vol.  xlvii., 

p.  426,  1903.) 
Zustandsanderungen  derMetalle  infolge  vonFestigkeitsbeanspruchungen, 

by  A.  MARTENS.     (Preuss.  Akad.  Wiss.  Berlin,  Sitz,  Ber.  ii.,  1910.) 
Wicksteed    Machine.      See  Proc.   Inst.   Mech.    Eng.,    1907   (Electrical 

control),  and  Proc.  Inst.  Mech.  Eng.,  1882  and  1891  (older  type). 
Extensometers.     (Eeport  of  British  Assoc.,  1896.) 
Measurement  of  Strains.     MORROW.    (Proceedings  Inst.  Mech.  Engineers, 

1904.) 
Tensile  Strength  of  Open  Hearth  Steel.    H.  H.  CAMPBELL.     ("  Science 

Abstracts,"  Jan.  1905.) 
Widmonstatten  Figures  in  Steel  Castings  (Microstructure,  &c.)     J.  O. 

ARNOLD  and  A.  McWiLLiAM.     (Nature,  Nov.  10th,  1904.) 
Cement   Exhibits   at    the    St.    Louis   Exhibition.      (Engineering   News, 

Nov.  10th,  1904.) 
Strength  and   Testing  of   Timber.     T.   HUDSON  BEARE.     (Engineering, 

Dec.  9th,  1904.) 
Yanadium    Steels.      L.    GUILLET.       ("Eevue    de    Metallurgie,"   Oct., 

1904.) 
Tests  on   Concrete   Steel  Beams.      J.  J.  KAHN.      (Engineering  Record, 

Oct.  8th,  1904.) 
Punching  as  a  Method  of  Testing.     L.  BACLE.     (Soc.  d'Encouragement, 

Bull.  vol.  cvi.,  Nov.  1904.) 
Special  Industrial  Steels.     H.  LE  CHATALIER.     (Soc.  d'Encouragement ; 

Revue  de  Metallurgie,  Nov.  1904.) 
Impact  Tests  of  Steel.      A.  E.  SEATON  and  A.   JUDE.      (Engineering, 

Nov.  25th,  1905.) 

Materials  which  Eetard  the  Setting  of  Portland  Cement.     E.  C.  CAR- 
PENTER.    (Engineering  Record,   Dec.  31st,  1904;  Engineering  News, 

Jan.  5th,  1905.) 
Eussian  Standards  for  Portland  Cement.    (Eiga-Ind.  Zeit,  vol.  xxx.,  p.  189, 

1904.) 
Toughness  of    Steel  after  Working   at   a   Blue   Heat.       C.   FREMONT. 

("  Comptes  Eendus,"  Dec.  12th,  1904.) 


268  BIBLIOGRAPHY 

Properties  of  Hard- Silicon  Steel  (Soc.  d' Encouragement,  vol.  w\.,Rei-uede 

Metallurgie,  Dec.  1904.) 

Drop  Testing  Machine.    W.  T.  M.  Goss.    (Pages  Weekly,  Jan.  13th,  1905.) 
Impact  Tests  of  Steel.     (Proc.  Inst.  Mech.  Eng.,  pp.  1135-1168,  July, 

1904.) 
Heat    Treatment    of   Chrome -Vanadium  Steel.      (Ibid,.,  pp.   1235-1282, 

July,  1904.) 
Hard-drawn   Copper  Wire.     T.    B.   DOOLITTLE.      (Harvard  Engineering 

Journal,  pp.  133-134,  Nov.  1905.) 
Hard-drawn   Copper  Wire.       T.  BOLTOX.      (Electrical  Review,  vol.   lx., 

pp.  131-133,  Jan.  25th,  1907.) 
Specification  of  Hard-drawn   Copper  Wire.     (Electric  Railway  Journal, 

vol.  xxxiv.,  pp.  181-183,  July  31st,  1909.) 
A  Heat  Treatment  Study  of  Bessemer  Steels.      ANDREW  McWiLLiAM 

and   ERNEST   J.    BARNES.     (Iron  and  Steel  Institute,   May   20th, 

1909.) 
The    Elastic  Breakdown   of   Materials,    subjected  to  Compound  Stress. 

L.  B.  TURNER,  B.A.     (Engineering,  Feb.  5th,  1909.) 
Notes  on  Tests  for  Hardness.       PROF.  T.  TURNER,  M.Sc.       (Iron   and 

Steel  Institute,  May  14th,  1909.) 

Ductile  Materials  under  Stress.     C.  A.  M.   SMITH,  M.Sc.     (Junior  In- 
stitution of  Engineers,  May,  1909.) 
Some    Experiments    on   Impact.        J.   E.   SEARS,   Jun.        (Engineering, 

April  30th,  1909  ;  May  7th,  1909.) 

The  Collapse  of  Tubes  under  External  Stress.      S.  E.  SLOCUM,  (Engineer- 
ing, Jan.  8th,  1909.) 

Guest's  Law  of  Combined  Stress.     C.  A.  M.  SMITH,  M.Sc.     (Engineer- 
ing, April  23rd,  1909.) 
Comparison  of  Tensile  Impact-Tensile  and  Repeated-Bending  Methods 

of  Testing  Steel.     (Inst.  Mech.  Eng.,  May  27th,  1910  ;  Engineering, 

June  3rd,  1910.) 
Research  on  the  Hardening  of  Carbon  and  Low  Tungsten  Tool  Steels. 

SHIPLY    N.    BRAYSHAW.      (Inst.    Mech.   Eng.,   April    15th,    1910; 

Engineering,  April  22nd,  1910.) 
Mechanical  Tests  of  Insulator  Porcelain  and  Glass.      R.  P.  CLARKSON. 

(Electrical  World,  vol.  Ivi.,  pp.  25-27  ;  July  7th,  1910.) 
Anomalous  Effects  on  First  Loading  a  Wire,  and  some  Effects  of  Bending 

Overstrain  in  Soft  Iron  Wires.    A.  I.  STEVENS,  M.A.,  B.Sc.     (Phil. 

Mag.,  April,  1910.) 
The  Breakdown  of  Tubes  under  Combined  Stress.     J.  J.  GUEST.     (Phil. 

Mag.,  1900.) 

Experiments  on  Combined  Stress.     PROF.  HANCOCK.     (PA/7.  Mag.,  1906.) 
Ductile  Material  under  Combined  Stress.     W.  A.  SCOBLE,  B.Sc.     (Phil. 

Mag.,  1906.) 
Brittle  Material  under  Combined  Stress.     W.  A.  SCOBLE,  B.Sc. 

Mag.,  1906.) 


BIBLIOGEAPHY  269 

Strength  of  Pipes  and  Cylinders.     C.  A.  M.  SMITH.     (Engineering,  March, 

1909.) 
Elastic  Breakdown  of  Non-Ferrous   Metals.     (Proc.  Inst.  Metals;  and 

Engineering,  1909.) 
A  Method  of  Detecting  the  Bending  of  Columns.    C.  A.  M.  SMITH,  M.Sc. 

(Inst.  Mech.  Eng.,  1908.) 
Mild    Steel   Tubes  in  Compression    and    under  Combined  Stress.     W. 

MASON,  M.Sc.     (Proc.  Inst.  Mech.  Eng.,  1910.) 
Elastic  Breakdown  of  Certain  Steels.     C.  A.   M.  SMITH,  M.Sc.    (Journal 

Iron  and  Steel  Institute,  1910.) 

Compound  Stress  Experiments.     (Proc.  Inst.  Mech.  Eng.,  1910.) 
Beports  of  Alloys  Research  Committees.     (Proc.  Inst.  Mech.  Eng.,  1891 

onwards.) 

(Post- graduates  about  to  commence  a  research  should  carefully  look  through 
Journals  mentioned  above  before  commencing  experiments.] 

The  Elastic  Limit  of  Manganese  and  other  Bronzes.    J.  A.  CAPP.    (Amer. 

Soc.  Mech.  Eng.,  1910.) 
Some  Experiments  on  Solid  Steel  Bars  under  Combined  Stress.    C.  A.  M. 

SMITH,  M.Sc.     (Engineering,  Aug.,  1909.) 
The  Stresses  in  a  Thick  Hollow  Cylinder  subjected  to  Internal  Pressure. 

L.  B.  TURNER,  B.A.     (Trans.  Cambridge  Phil.  Soc.,  Sept.  1910.) 
Further  Tests  of  Brittle  Materials  under  Combined  Stress.   W.  A.  SCOBLE, 

B.Sc.     (Phil.  Mag.,  June,  1910.) 
The  Design  of  Struts.      W.  E.  LILLY,  M.A.,  D.Sc.      (Engineering,  Jan. 

1908.) 

The  Behaviour  of  Ductile  Material  under  Torsional  Strain  with  Restora- 
tion of  Elasticity  at  Low  Temperatures.     C.  E.  LARARD,  A.M.I.C.E. 

(Proc.  Inst.  C.E.,  vol.  179,  p.  3,  1910.) 
An  Experimental  Investigation  into  the  Flow  of  Rocks.     F.  D.  ADAMS 

and  E.  G.  COKER.     (Amer.  Journ.  Sci.,  June,  1910.) 
The  Elastic  Properties  of  Platinum -Iridium  Wires.     K.  E.  GUTHE  and 

L.  P.  LIEG.     (Physical  Review,  May,  1910.) 
Tesfs  of  Concrete   Columns   made  under  Building  Conditions.     H.  C. 

BERRY.     (Engineering  Record,  Feb.,  1910.) 
Untersuchung  eines  im  Betriebe  geplatzten  Siedevohrs.     E.  HEYN  and 

0.  BAUER.     (Konigl.  Materialpriifungsamt.) 
Berechnung  Zylindrischev  Druckfedeon  auf  Sicherheit  gegen  seitliches 

Ausknicken.     E.  HURLBRINK.     (Zeitschr.  Vereines.  Deutsch.,  Jan., 

1910.) 


USEFUL   CONSTANTS. 


1  Inch=2iv40  millimetres. 

1  Gallon  =  -1604  cubic  foot=10  Ib.  of  water  at  62°  F. 

Weight  of  1  Ib.  in  London=445,000  dynes. 

One  pound  avoirdupois =7 000  grains=453'6  grammes. 

One  cubic  foot  of  water  weighs  62 -3  Ib. 

A  column  of  water  2'3  feet  high  corresponds  to  a  pressure  of  1  Ib.  per 

in. 

Absolute  temp.,  t=0°  C.+2730  or  0°F.-f460°. 
One  radian =57 '30  degrees. 

To  convert  common  into  Napierian  logarithms,  multiply  by  2-3026. 
The  base  of  the  Napierian  logarithms  is  e=2'7183. 
The  value  of  g  at  London =32 '182  feet  per  sec.  per  sec. 


USEFUL   CONSTANTS 


271 


LOGARITHMS. 


0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

0000 

0043 

0086 

0128 

0170 

0212 

0253 

0294 

0334 

0374 

4  9  13  17 
4  8  12  16 

20 

26  30  34  38 
24  28  82  37 

11 

0414 

0453 

0492 

0531 

0569 

0607 

0645 

0682 

0719 

0755 

4  8  12  15 
4  7  11  15 

19 
19 

23  27  31  35 
22  26  30  33 

12 

0792 

0828 

0864 

0899 

0934 

0969 

1004 

1038 

1072 

1106 

3  7  11  14 
3  7  10  14 

18 
17 

21  25  28  32 
20  24  27  31 

13 

1139 

1173 

1206 

1239 

1271 

1303 

1335 

1367 

1399 

1430 

3  7  10  13 
3  7  10  12 

16 
16 

20  23  26  30 
19  22  25  29 

14 

1461 

1492 

1523 

1553 

1584 

1614 

1644 

1673 

1703 

1732 

3  6  9  12 
3  6  9  12 

15 
15 

18  21  24  28 
17  20  23  26 

15 

17-61 

1700 

1818 

1847 

1875 

1903 

1931 

1959 

1987 

2014 

3  6  9  11 
3  5  8  11 

14 
14 

17  20  23  26 
16392225 

16 

2041 

2068 

2095 

2122 

2148 

2175 

2201 

2227 

2253 

2279 

3  5  8  11 
3  5  8  10 

14 

13 

16  19  22  24 
15  18  21  23 

17 

2304 

2330 

2355 

2380 

2405 

2430 

2455 

2480 

2504 

2529 

3  5  8  10 
2  5  7  10 

13 
12 

15  18  20  23 
15  17  19  22 

18 

2553 

2577 

2601 

2625 

2648 

2672 

2695 

2718 

2742 

2765 

2579 
2579 

12 
11 

14  16  39  21 
14161821 

19 

2788 

2810 

2833 

2856 

2878 

2900 

2923 

2945 

2967 

2989 

2479 
2468 

11 

11 

13  16  18  20 
13  15  17  19 

20 

3010 

3032 

3054 

3075 

3096 

3118 

3139 

3160 

3181 

3201 

2468 

11 

13  15  17  19 

21 
22 
23 
24 

3222 
3424 
3(517 
3802 

3243 
3444 
3636 
3820 

3263 
3464 
3655 
3838 

3284 
3483 
3674 
3856 

3304 

3502 
3C92 
3874 

3324 
3522 
3711 
3892 

3345 
3541 
3729 
3909 

3365 
3560 
3747 
8927 

3385 
3579 
3766 
3945 

3404 
3598 
3784 
3962 

2468 
2468 
2467 
2457 

10 
10 
9 
9 

121416  18 
12  14  15  17 
11  131517 
11  12  14  16 

25 

3979 

3997 

4014 

4031 

4048 

4065 

4082 

4099 

4116 

4133 

2357 

9 

10  12  14  15 

26 
27 
28 
29 

4150 
4314 
4472 
4624 

4166 
4330 

4487 
4639 

4183 
4346 
4502 
4654 

4200 
4362 
4518 
4669 

4216 
4378 
4533 
4683 

4232 
4393 
4548 
4698 

4249 
4409 
4564 
4713 

4265 
4425 
4579 

4728 

4281 
4440 
4594 
4742 

4298 
4456 
4609 
4757 

2357 
2356 
2356 
1346 

8 
8 
8 

7 

10  11  13  15 
9  11  13  14 
9  11  12  14 
9  10  12  13 

30 

4771 

4786 

4800 

4814 

4829 

4843 

4857 

4871 

4886 

4900 

1346 

7 

9  10  11  13 

31 
32 
33 
34 

4914 
5051 
5185 
5315 

4928 
5065 
5198 
53-28 

4942 
5079 
5211 
5340 

4955 
5092 
5224 
5353 

4969 
5105 
5237 
5366 

4983 
5119 
5250 
5378 

4997 
5132 
5263 
5391 

5011 
5145 
5276 
5403 

5024 
5159 
5289 
5416 

5038 
5172 
5302 
5428 

1346 
1345 
1345 
1345 

7 
7 
6 
6 

8  10  11  12 
8    9  11  12 
8    9  10  12 
8    91011 

35 

5441 

5453 

5465 

5478 

5490 

5502 

5514 

5527 

5539 

5551 

1245 

6 

7    9  10  11 

36 
37 
38 
39 

5563 
5682 
5798 
5911 

5575 
5694 
5809 
5922 

5587 
5705 
5821 
5933 

5599 
5717 
5832 
5944 

5611 

5729 
5843 
5955 

5623 
5740 
5855 
5966 

£635 
5752 
5866 
5977 

5647 
5763 

5877 
5988 

5658 
5775 
5888 
5999 

5670 
57S6 
5899 
6010 

1245 
1235 
1235 
1234 

6 

8 
6 
5 

7    81011 
7    8    910 
7    8    9  10 

7    8    910 

40 

6021 

6031 

6042 

6053 

6064 

6075 

6085 

6096 

6107 

6117 

1234 

5 

6    8    910 

41 
42 
43 
44 

6128 
6232 
6335 
6435 

6138 
6243 
6345 
6444 

6149 
6253 
6355 
6454 

6160 
6263 
6365 
6464 

6170 

6274 
6375 
6474 

6180 
6284 
6385 
6484 

6191 
6294 
6395 
6493 

6201 
6304 
6405 
6503 

6212 
63*14 
6415 
6513 

6222 
6325 
6425 
6522 

1234 
1234 
1234 
1234 

5 
5 
5 

5 

6789 
6789 
6789 
6789 

45 

6532 

6542 

6551 

6561 

6571 

6580 

6590 

6599 

6609 

6618 

1234 

5 

6789 

46 
47 
48 
49 

6628 
6721 
6812 
6902 

6637 
6730 
6821 
6911 

6646 
6739 
6830 
6920 

6656 

6749 
6839 
C92S 

6665 
6758 
6848 
6937 

6675 
6767 
6857 
6946 

6684 
6776 
6866 
6955 

6693 
6785 
6875 
6964 

6702 
6794 

6884 
6972 

6712 
6803 
6893 
6981 

1234 
1234 
1234 
1234 

5 
5 
4 
4 

6778 
5678 
5678 

5678 

50 

6990 

0998 

7007 

7016 

7024 

7033 

7042 

7050 

7059 

7067 

1233 

4 

5678 

272 


USEFUL  CONSTANTS 


LOGARITHMS. 


0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

1234 

5 

6789 

51 
52 
53 
54 

7076 
7160 
7243 
7324 

7084 
7168 
7251 
7332 

7093 
7177 
7259 
7340 

7101 
7185 
7267 
7348 

7110 

7193 
7275 
7356 

7118 
7202 
7284 
7364 

7126 
7210 
7292 
7372 

7135 
7218 
7300 
7380 

7143 

7226 
7308 
7388 

7152 

73K 
7396 

1233 
1223 
1223 
1223 

4 
4 
4 
4 

5678 
5677 
5667 
5667 

55 

7404 

7412 

7419 

7427 

7435 

7443 

7451 

7459 

7466 

7474 

1223 

4 

5567 

56 
57 
58 
59 

7482 
7559 
7634 
7709 

7490 
7566 
7642 
7716 

7497 
7574 
7649 
7723 

7505 

7582 
7657 
7731 

7513 
7589 
7664 
7738 

7520 
7597 
7672 
7745 

7528 
7604 
7679 
7752 

7536 
7612 
7686 
7760 

7543 
7619 
7694 
7767 

7551 
7627 
7701 
7774 

1223 
1223 
1123 
1123 

4 
4 
4 
4 

5567 
5567 
4567 
4567 

60 

7782 

7789 

7796 

7803 

7810 

7818 

7825 

7832 

7831) 

7846 

1123 

4 

456  6 

61 
62 
63 
64 

7853 
7924 
7993 
8062 

7860 
7931 
8000 
8069 

7868 
7938 
8007 
8075 

7875 
7945 
8014 
8082 

7882 
7932 
8021 
8089 

7889 
7959 
8028 
8096 

7896 
7966 
8035 
8102 

7903 
7973 
8041 
8109 

7910 
7980 
8048 
8116 

7917 
7987 
8055 
8122 

1123 
1123 
1123 
1123 

4 
3 
3 
3 

4  5  C)  6 
4566 
4556 
4556 

65 

8129 

8136 

8142 

8149 

8156 

8162 

8169 

8176 

8182 

8189 

1123 

3 

4556 

66 
67 
68 
69 

8195 
8261 
8325 

8388 

8202 
8267 
8331 
8395 

8209 
8274 
8338 
8401 

8215 
8280 
8344 
8407 

8222 
8287 
8351 
8414 

8228 
8293 
8357 
8420 

8235 
8299 
8363 
8426 

8241 
8306 
8370 
8432 

8248 
8312 
8376 
8439 

8254 
8319 
8382 
8445 

1123 
1123 
1123 
1122 

3 
3 
3 
3 

4556 
4550 
4456 
4456 

70 

8451 

8457 

8463 

8470 

8476 

8482 

8488 

8494 

8500 

8506 

1122 

3 

4  4  5  6 

71 
72 
73 
74 

8513 
8573 
8633 
8692 

8519 
8579 
8639 
8698 

8525 
8585 
8645 
8704 

8531 
8591 
8651 
8710 

8537 
8597 
8657 
8716 

8543 
8603 
8633 
8722 

8549 
8609 
8669 
8727 

8555 
8615 
8675 
8733 

8561 
8621 
8681 
8739 

8567 
8627 
8686 
8745 

1122 
1122 
1122 
1122 

3 

a 

3 
3 

4455 
4455 
4  4  5  5 

4  4  r.  r, 

75 

8751 

8756 

8762 

8768 

8774 

8779 

8785 

8791 

8797 

8802 

1122 

3 

3  4  5  5 

76 
77 
78 
79 

85:08 
8865 
8921 
8976 

8814 
8871 
8927 
8982 

8820 
Sb76 
8932 
8987 

8825 
8882 
8938 
8993 

8831 
8887 
8943 
8998 

8837 
8893 
8949 
9004 

8842 
8899 
8954 
9009 

8848 
8904 
8960 
9015 

8854 
8910 
8965 
9020 

8859 
8915 
8971 
9025 

1122 
1122 
1122 
1122 

3 
3 
3 
3 

3455 
3445 
3445 
344:. 

80 

9031 

9036 

9042 

9047 

9053 

9058 

9063 

9069 

9074 

9079 

1122 

3 

3445 

81 
82 
83 
84 

9085 
9138 
9191 
9243 

9090 
9143 
9196 
9248 

9096 
9149 
9201 
9253 

9101 
9154 
9206 
9258 

9106 
9159 
9212 
9263 

9112 
9165 
9217 
9269 

9117 
9170 
9222 
9274 

9122 
9175 
9227 
9279 

9128 
9180 
9232 

9284 

9133 
9186 
9238 
9289 

1122 
1122 
1122 
1122 

3 
3 
3 
3 

3445 

3445 
3445 
3445 

85 

9294 

9299 

9304 

9309 

9315 

9320 

9325 

9330 

9335 

9340 

1122 

3 

3445 

86 
87 
88 
89 

9345 
9395 
9445 
9494 

9350 
9400 
9450 
9499 

9355 
9405 
9455 
9504 

9360 
9410 
9460 
9509 

9365 
9415 
9465 
9513 

9370 
9420 
9469 
9518 

9375 
9425 
9474 
9523 

9380 
9430 
9479 
9528 

9385 
9435 
9484 
9533 

9390 
9440 
9489 
9538 

1122 
0112 
0112 
0112 

3 
2 

2 
2 

3  4  4  5 
3344 
3344 
3344 

90 

9542 

9547 

9552 

9557 

9562 

9566 

9571 

9576 

9581 

9586 

0112 

2 

3344 

91 
92 
93 
94 

9590 
9638 
9685 
9731 

9595 
9643 
9689 
9736 

9600 
9647 
9694 
9741 

9605 
9652 
9699 
9745 

9609 
9657 
9703 
9750 

9614 
9661 
9708 
9754 

9619 
9666 
9713 
9759 

9624 
9671 
9717 
9763 

9628 
9675 
9722 
9768 

9633 
9680 
9727 
9773 

0112 
0112 
0112 
0112 

2 
2 

2 

3344 
3344 
3344 
3344 

95 

9777 

9782 

97-6 

9791 

9795 

9800 

9805 

9809 

9814 

9818 

0112 

2 

3344 

96 
97 
98 
99 

9823 
9868 
9912 
9956 

9827 
9872 
9917 
9961 

9832 
9877 
9^21 
9965 

9836 
9881 
9926 
9969 

9841 
9886 
9930 
9974 

9845 
9890 
9934 

9978 

9850 
0894 
9939 
9983 

9854 
9899 
9943 

9987 

9859 
9903 
9948 
9991 

9863 
9908 
9952 
9996 

0112 
0112 
0112 
0112 

2 
2 
o 

3344 
3344 
3  3  4  4 
3334 

USEFUL   CONSTANTS 

ANTILOGARITHMS. 


273 


g 

•00 

1000 

1002 

1005 

1007 

1009 

1012 

1014 

1016 

1019 

1021 

0011 

1 

1222 

•01 
•02 
•03 
•04 

1023 
1047 
1072 
1096 

1026 
1050 
1074 
1099 

1028 
1052 
1076 
1102 

1030 
1054 
1079 
1104 

1033 
1057 
1081 
1107 

1035 
1059 
1084 
1109 

1038 
1062 
1086 
1112 

1040 
1064 
1089 
1114 

1042 
1067 
1091 
1117 

1045 
1069 
1094 
1119 

0011 
0011 
0011 
0111 

1 
1 
1 
1 

1222 
1222 
1222 
2222 

•03 

1122 

1125 

1127 

1130 

1132 

1135 

1138 

1140 

1143 

1146 

0111 

1 

2222 

•06 
•07 
•08 
•09 

1148 
1175 
1202 
1230 

1151 
1178 
1205 
1233 

1153 
1180 
1208 
1236 

1156 
1183 
1211 
1239 

1159 
1186 
1213 
1242 

1161 
1189 
1216 
1245 

1164 
1191 
1219 
1247 

1167 
1194 
1222 
1250 

1169 
1197 
1225 
1253 

1172 
1199 
1227 
1256 

0111 
0111 
0111 
0111 

1 
1 
1 
1 

2222 
2222 
2223 
2223 

•10 

1259 

1262 

1265 

1268 

1271 

1274 

1276 

1279 

1282 

1285 

0111 

1 

2223 

•11 
•12 
•13 
•14 

1288 
1318 
1349 
1380 

1291 
1321 
1352 
1384 

1294 
1324 
1355 
1387 

1297 
1327 
1358 
1390 

1300 
1330 
1361 
1393 

1303 
1334 
1365 
1396 

1306 
1337 
1368 
1400 

1309 
1340 
1371 
1403 

1312 
1343 
1374 
1406 

1315 
1346 
1377 
1409 

0111 
0111 
0111 
0111 

2 
2 
2 
2 

2223 
2223 
2233 
2233 

•15 

1413 

1416 

1419 

1422 

1426 

1429 

1432 

1435 

1439 

1442 

0111 

2 

2233 

•16 
•17 
•18 
•19 

1445 
1479 
1514 
1549 

1449 
1483 
1517 
1552 

1452 
1486 
1521 
1556 

1455 
1489 
1524 
1560 

1459 
1493 
1528 
1563 

1462 
1496 
1531 
1567 

1466 
1500 
1535 
1570 

1469 
1503 
1538 
1574 

1472 
1507 
1542 
1578 

1476 
1510 
1545 
1581 

0111 
0111 
0111 
0111 

2 

2 
2 

2 

2233 
2233 
2233 
2333 

•20 

1585 

1589 

1592 

1596 

1600 

1603 

1607 

1611 

1614 

1618 

0111 

2 

2333 

•21 
•22 
•23 
•24 

1622 
1660 
1698 
1738 

1626 
1663 
1702 
1742 

1629 
1667 
1706 
1746 

1633 
1671 
1710 
1750 

1637 
1675 
1714 
1754 

1641 
1679 
1718 
1758 

1644 
1683 
1722 
1762 

1648 
1687 
1726 
1766 

1652 
1690 
1730 
1770 

1656 
1694 
1734 
1774 

0112 
0112 
0112 
0112 

2 
2 
2 
2 

2333 
2333 
2334 
2334 

•23 

1778 

1782 

1786 

1791 

1795 

1799 

1803 

1807 

1811 

1816 

0112 

2 

2334 

•26 
•27 
•28 
•29 

1820 
1862 
1905 
1950 

1824 
1866 
1910 
1954 

1828 
1871 
1914 
1959 

1832 
1875 
1919 
1963 

1837 
1879 
1923 
1968 

1841 

1884 
1928 
1972 

1845 
1888 
1932 
1977 

1849 
1892 
1936 
1982 

1854 
1897 
1941 
1986 

1858 
1901 
1945 
1991 

0112 
0112 
0112 
0112 

2 
2 
2 
2 

3334 
3334 
3344 
3344 

•30 

1995 

2000 

2004 

2009 

2014 

2018 

2023 

2028 

2032 

2037 

0112 

2 

3344 

•31 
•32 
•33 
•34 

2042 

2089 
2138 
2188 

2046 
2094 
2143 
2193 

2051 
2099 
2148 
2198 

2056 
2104 
2153 
2203 

2061 
2109 
2158 
2208 

2065 
2113 
2163 
2213 

2070 
2118 
2168 
2218 

2075 
2123 
2173 
2223 

2080 
2128 
2178 
2228 

2084 
2133 
2183 
2234 

0112 
0112 
0112 
1122 

2 

3344 
3344 
3344 
3445 

•35 

2239 

2244 

2249 

2254 

2259 

2265 

2270 

2275 

2280 

2286 

1122 

3 

3445 

•36 
•37 
•38 
•39 

2291 
2344 
2399 
2455 

2296 
2350 
2404 
2460 

2301 
2355 
2410 
2466 

2307 
2360 
2415 
2472 

2312 
2366 
2421 
2477 

2317 
2371 
2427 
2483 

2323 
2377 
2432 
2489 

2328 
2382 
2438 
2495 

2333 
2388 
2443 
2500 

2339 
2393 
2449 
2506 

1122 
1122 
1122 
1122 

3 
3 
3 
3 

3445 
3445 
3445 
3455 

•40 

2512 

2518 

2523 

2529 

2535 

2541 

2547 

2553 

2559 

2564 

1122 

3 

4455 

•41 
•42 
•43 
•44 

2570 
2630 
2692 

2754 

2576 
2636 
2698 
2761 

2582 
2642 
2704 
2767 

2588 
2649 
2710 
2770 

2594 
2655 
2716 
2780 

2600 
2661 
2723 
2786 

2606 
2667 
2729 
2793 

2612 
2673 
2735 
2799 

2618 
2679 
2742 
2805 

2624 

2885 
2748 
2812 

1122 

1122 
1123 
1123 

3 
3 
3 
3 

4455 
4456 
4456 
4456 

•43 

2818 

2825 

2831 

2838 

2844 

2851 

2858 

2864 

2871 

2877 

1123 

3 

4556 

•46 
•47 
•48 
•49 

2884 
2951 
3020 
3090 

2891 
2958 
3027 
3097 

2897 
2965 
3034 
3105 

2904 
2972 
3041 
3112 

2911 
2979 
3048 
3119 

2917 
2985 
3055 
3126 

2924 
2992 
3062 
3133 

2931 
2999 
3069 
3141 

2938 
3006 
3076 
3148 

2944 
3013 
3083 
3155 

1123 
1123 
1123 
1123 

3 
3 
4 

4 

4556 
4556 
4566 
4566 

T.M. 


274 


USEFUL  CONSTANTS 

ANTILOGARITHMS. 


6789 

•50 

3162 

3170 

3177 

3184 

3192 

3199 

3206 

3214 

3221 

3228 

1123 

4 

4  f>  6  7 

•51 
•52 
•53 
•51 

3226 
3311 
3388 
3467 

3243 
3319 
3396 
3475 

3251 
3327 
3404 
3483 

8268 

3334 
3412 
3491 

3266 
3342 
3420 
3499 

3273 
3350 
3428 
3508 

3281 
3357 
3436 
3516 

3289 
3365 
3443 
3524 

3296 
3373 
3451 
3532 

6304. 
3381 
3459 
3540 

1223 
1223 
1223 
1223 

4 

4 
4 

4 

5567 
5567 
5667 
5  6  6  7 

•55 

3548 

3556 

3565 

3573 

3581 

3589 

3597 

3606 

3614 

3622 

1223 

4 

5677 

•56 
•57 
•58 
59 

3631 
3715 
3802 
3890 

3639 
3724 
3811 
3899 

3648 
3733 
3819 
3908 

3656 
3741 
3828 
3917 

3664 
3750 
3837 
3926 

3673 
3758 
3846 
3936 

3681 
3767 
3855 
3945 

3690 
3776 
3864 
3954 

3698 
3784 
3873 
3963 

3707 
3793 

3882 
3972 

1233 
1233 
1234 
1234 

4 
4 
4 
5 

5678 
5678 
5678 
5678 

•60 

3981 

3990 

3999 

4009 

4018 

4027 

4036 

4046 

4055 

4064 

1234 

5 

6678 

•61 
•62 
•63 
•64 

4074 
4169 
4266 
4365 

4083 
4178 
4276 
4375 

4093 
4188 
4285 
4385 

4102 
4198 
4295 
4395 

4111 
4207 
4305 
4406 

4121 
4217 
4315 
4416 

4130 
4227 
4325 
4426 

4140 
4236 
4335 
4436 

4150 
4246 
4345 
4446 

4159 
4256 
4355 
4457 

1234 
1234 
1234 
1234 

5 

5 
5 
5 

6789 
6789 
6789 
6789 

•65 

4467 

4477 

4487 

4498 

4508 

4519 

4529 

4539 

4550 

4560 

1234 

5 

6789 

•66 
•67 
•68 
•69 

4571 
4677 
4786 
4898 

4581 
4688 
4797 
4909 

4592 
4699 
4808 
4920 

4603 
4710 
4819 
4932 

4613 
4721 
4831 
4943 

4624 
4732 
4842 
4955 

4634 
4742 
4853 
4966 

4645 
4753 
4864 
4977 

4656 
4764 
4875 
4989 

4667 
4775 
4887 
5000 

1234 
1234 
1234 
1235 

5 
5 
6 
6 

6  7  9  10 
7  8  9  10 
7  8  9  10 
7  8  9  10 

•70 

5012 

5023 

5035 

5047 

5058 

5070 

5082 

5093 

5105 

5117 

1245 

6 

7  8  9  11 

•71 
•72 
•73 
•74 

5129 
5248 
5370 
5495 

5140 
5260 
5383 
5508 

5152 
5272 
5395 
5521 

5164 
5284 
5408 
5534 

5176 
5297 
5420 
5546 

5188 
5309 
5433 
5559 

5200 
5321 
5445 
5572 

5212 
5333 
5458 
5585 

5224 
5346 
5470 
5598 

5236 
5358 
5483 
5610 

1245 
1245 
1345 
1345 

6 
6 
6 
6 

7  8  10  11 
7  9  10  11 
8  9  10  11 
8  9  10  12 

•75 

5623 

5636 

5649 

5662 

5675 

5689 

5702 

5715 

5728 

5741 

1345 

7 

8  9  10  12 

•76 
•77 
•78 
•79 

5754 
5888 
6026 
6166 

5768 
5902 
6039 
6180 

5781 
5916 
6053 
6194 

5794 
5929 
6067 
6209 

5808 
5943 
6081 
6223 

5821 
5957 
6095 
6237 

5834 
5970 
6109 
6252 

5848 
5984 
6124 
6266 

5861 
5998 
6138 
6281 

5875 
6012 
6152 
6295 

1345 
1345 
1346 
1346 

7 
7 

7 
7 

8  9  11  12 
8  10  11  12 
8  10  11  13 
9  10  11  13 

•80 

6310 

6324 

6339 

6353 

6368 

6383 

6397 

6412 

6427 

6442 

1346 

7 

9  10  12  13 

•81 
•82 
•83 

•84 

6457 
6607 
6761 
6918 

6471 
6622 
6776 
6934 

6486 
6637 
6792 
6950 

6501 
6653 
6808 
6966 

6516 
6668 
6823 
6982 

6531 
6683 
6839 
6998 

6546 
6699 
6855 
7015 

6561 
6714 
6871 
7031 

6577 
6730 
6887 
7047 

6592 
6745 
6902 
7063 

2356 
2356 
2356 
2356 

8 
8 
8 
8 

9  11  12  14 
9  11  12  14 
9  11  13  14 
10  11  13  15 

•85 

7079 

7096 

7112 

7129 

7145 

7161 

7178 

7194 

7211 

7228 

2357 

8 

10  12  13  15 

•86 
•87 
•88 
•89 

7244 
7413 
7586 
7762 

7261 
7430 
7603 
7780 

7278 
7447 
7621 
7798 

7295 
7464 
7638 
7816 

7311 

7482 
7656 
7S34 

7328 
7499 
7674 
7852 

7345 
7516 
7691 
7870 

7362 
7534 
7709 
7889 

7379 
7551 
7727 
7907 

7396 
7568 
7745 
7925 

2357 
2357 

2457 
2457 

8 
9 
9 
9 

10  12  13  15 
10  12  14  16 
11  12  14  16 
11  13  14  16 

•90 

7943 

7962 

7980 

7998 

8017 

8035 

8054 

8072 

8091 

8110 

2467 

9 

11  13  15  17 

•91 
•92 
•93 
•94 

8128 
8318 
8511 
8710 

8147 
8337 
8531 
8730 

8166 
8356 
8551 
8750 

8185 
8375 
8570 
S770 

8204 
8395 
8590 
8790 

8222 
8414 
8610 
8810 

8241 
8433 
8630 
8831 

8260 
8453 
8650 
8851 

8279 
8472 
8670 
8872 

8299 
8492 
8690 
8892 

2468 
2468 
2468 

2468 

9 
10 
10 
10 

11  13  15  17 
12  14  15  17 
12  14  16  18 
12  14  16  18 

•95 

8913 

8933 

8954 

8974 

8995 

9016 

9036 

9057 

9078 

9099 

2468 

10 

12  15  17  19 

96 
•97 
•98 
•99 

9120 
9333 
0550 

9772 

9141 
9354 

9572 
9795 

9162 
9376 
9594 
9817 

9183 
9397 
9616 
9840 

9204 
9419 
9638 
9863 

9226 
9441 
9661 
9886 

9247 
9462 
9683 
9908 

9268 
9484 
9705 
9931 

9290 
9506 
9727 
9954 

9311 
9528 
9750 
9977 

2468 
2479 
2479 
2579 

11 
11 
11 
11 

13  15  17  19 
13  15  17  20 
13  16  18  20 
14  16  18  20 

USEFUL  CONSTANTS 


275 


Angle. 

Chord. 

Sine. 

Tangent. 
0 

Co-tangent. 

90 

57-2900 
28-6363 
19-0811 
14-3007 

Cosine. 

1-5708 

1-5533 
1-5359 
1-5184 
1-5010 

De- 
grees. 

0° 

1 

3 

4 

Radians. 

0 

•0175 
•0349 
•0524 
•0698 

0 

0 

1 

•9998 
•9994 
•9986 
•9976 

1-414 

90° 

•017 
•035 
•052 
•070 

•0175 
•0349 
•0523 
•0698 

•0175 
•0349 
•0524 
•0699 

1-402 
1-389 
1-377 
1-364 

89 
88 
87 
86 

5 

•0873 

•087 

•105 
•122 
•140 

•157 

•0872 

•0875 

11-4301 

9  5144 
8-1443 
7-1154 
6-3138 

•9962 

1-351 

1-338 
1-325 
1-312 
1-299 

1-4835 

1-4661 
1-4486 
1-4312 
1-4137 

85 

6 
7 
8 
9  ' 

•1047 
•1222 
•1396 
•1571 

•1045 
•1219 
•1392 
•1564 

•1051 
•1228 
•1405 
•1584 

•9945 
•9925 
•9903 

•9877 

84 
83 

82 
81 

10 

•1745 

•174 

•1736 

•1763 

5-6713 

•9848 

1-286 

1-3963 

80 

11 
12 

13 
14 

•1920 
•2094 
•2269 
•2443 

•192 
•209 
•226 
•244 

•261 

•1908 
•2079 
•2250 
•2419 

•1944 
•2126 
•2309 
•2493 

5-1446 
4-7046 
4-3315 
4-0108 

•9816 
•9781 
•9744 
•9703 

1-272 
1-259 
1-245 
1-231 

1-3788 
1-3614 
1-3439 
1-3265 

79 
78 
77 
76 

15 

•2618 

•2588 

•2679 

37321 

•9659 

1-218 

1-3090 

75 

16 
17 
IS 
19 

•2793 
•2967 
•3142 
•3316 

•278 
•296 
•313 
•330 

•347 

•2756 
•2924 
•3090 
•3256 

•3420 

•2867 
•3057 
•3249 
•3443 

3-4874 
3-2709 
3-0777 
2-9042 

•9613 
•9563 
•9511 
•9455 

1-204 
1-190 
1-176 
1-161 

1-2915 
1-2741 
1-2566 
1-2392 

74 
73 

72 
71 

70 

69 

68 
67 
66 

65 

64 
63 
62 
61 

60 

20 

•3491 

•3665 
•3840 
•4014 
•4189 

•4363 

•3640 

27475 

•9397 

1-147 

1-2217 

21 
22 

24 
25 

26 

27 
28 
29 

•364 
•382 
•399 
•416 

•3584 
•3746 
•3907 
•4067 

•3839 
•4040 
•4245 
•4452 

2-6051 
2-4751 
2-3559 
2-2460 

•9336 
•9272 
•9205 
•9135 

1-133 
1-118 
1-104 
1-089 

1-2043 
1-1868 
1-1694 
1-1519 

1-1345 

1-1170 
1-0996 
1-0821 
1-0647 

•433 

•4226 

•4663 

2-1445 

•9063 

•8988 
•8910 
•8829 
•8746 

1-075 

•4538 
•4712 
•4887 
•5061 

•5236 

•450 
•467 
•484 
•501 

•4384 
•4540 
•4695 
•4848 

•4877 
•5095 
•5317 
•5543 

2-0503 
1-9626 
1-8807 
1-8040 

1-060 
1-045 
1-030 
1-015 

30 

•518 

•5000 

•5774 

1-7321 

•8660 

1-000 

1-0172 

31 
32 
33 
34 

•5411 

•5585 
•5760 
•5934 

•6109 

•534 
•551 
•568 
•585 

•5150 
•5299 
•5446 
•5592 

•6009 
•6249 
•6494 
•6745 

1-6643 
1-6003 
1-5399 
1-4826 

•8572 
•8480 
•8387 
•8290 

•985 
•970 
•954 
•939 

1-0297 
1-0123 
•9948 
•9774 

59 

58 
57 
56 

55 

35 

•601 

•5736 

•7002 

1-4281 

•8192 

•923 

•9599 

36 
37 
38 
39 

•6283 
•6458 
•6632 
•6S07 

•618 
•635 
•651 

•668 

•5878 
•6018 
•6157 
•6293 

•7265 
•7536 
•7813 
•8098 

1-3764 
1-3270 
1-2799 
1-2349 

•8090 
•7986 
•7880 
•7771 

•908 
•892 
•877 
•861 

•9425 
•9250 
•9076 
•8901 

54 
53 
52 
51 

40 

•6981 

•684 

•6428 

•8391 

1-1918 

•7660 

•845 

•8727 

50 

41 

42 
43 
44 

•7156 
•7330 
•7505 
•7679 

•700 
•717 
•733 

•749 

•6561 
•6691 
•6820 
•6947 

•8693 
•9004 
•9325 
•9657 

1-1504 
1-1106 
1-0724 
1-0355 

•7547 
•7431 
•7314 
•7193 

•829 
•813 
•797 

•781 

•   '8552 
•8378 
•8203 
•8029 

49 
48 
47 
46 

45° 

•7854 

•765 

•7071 
Cosine. 

1-0000 

roooo 

Tangent. 

•7071 
Sine. 

•765 

•7854 
Radians. 

45° 

Co-tangent. 

Chord. 

De- 
grees. 

Angle. 

T    2 


INDEX 


A. 


ACCURACY  of  large  testing  machine, 

test  for,  47,  217 
Admiralty    specification     for    cast 

iron,    163 ;    for   machinery,  264 
Alloys,   new,    8 

Alloys  Eesearch  Committee,  143 
Alternate  tension  and  compression, 

220 
Alternating  stress  machines,    1 68  ; 

Arnold's,    175 ;    J.  H.    Smith's, 

178  ;  Stanton's,  177 
Alternating       torsion       machine, 

C.  A.  M.  Smith's,  182 
Aluminium,  8  ;    tension  tests    on, 

86  ;  effect    of    boiling  on  elastic 

properties  of,  128 
Amsler  testing  machine,  34 

Amsler  -  Laffon     beam    testing 

machine,  203 
Angle  of  twist,  117 
Annealing,  12 
Antimony,  235 

Appearance  of  compression  speci- 
men, 92 
Arnold,    Dr.     J.,     12,     168,     175, 

177,  260;      alternating       stress 

machine,  175 

Ashcroft's  extensometer,  56 
Attachment,    double    autographic, 

82 
Autographic  recorders,  72  ;  method, 

Kennedy's,  78;     diagram,     80; 

attachment,     double,     82 ;    dia- 
gram,  test      to     fracture  with, 

218 


Automatic  testing  machine.-;,  41 

A  very,  Messrs.  W.  and  T.,  Ltd.,  26, 
254 ;  testing  machine,  speci- 
fication of,  31 ;  torsion  machine, 
121 ;  impact  machine,  137 

Axial  loading,  the  problem  of,  46 
71 

Ayrton,  Prof.,  67 


13. 


BAILEY  transverse  testing  ma- 
chine, 39 ;  torsion  machine, 
119;  cement  testing  machine, 
193;  cement  crushing  machine, 
195 ;  testing  machine,  experi- 
ments with,  217 

Bairstow,  Mr.  Leonard,  103,  188 

Balance  weight,  to  check  the 
weight  of  the,  50 

Balls,  crushing  tests  of,  221 ; 
Brinell's  test  on,  147 

Barnes,  Mr.  E.  J.,  260 

Bauschinger,  25,  102,  181 ;  instru- 
ment, 62 

Beam  testing  machine,  164 

Beams,  deflection  of,  39  ;  breaking 
of,  220 ;  testing  of,  89,  220 ; 
shearing  tests  on  short,  221 

Bedding,  effect  of,  219 

Bending  tests,  arrangement  of  a 
machine  for,  39  stress  machines, 
172;  standard  angle  of,  186; 
effect  of  speed  on,  188 ;  and 
torsion  combined,  221,  251 

Benedicks  of  Upsala,  149 


278 


INDEX 


Berlin,  25 

Bessemer  steel,  heat  treatment  of, 

105,  260 

Bibliography,  265 
Birmingham,  University  of,  25 
Blount,     Kirkaldy    and     Sankey, 

Messrs.,  140 
Boiler,  combined  stress  in  a,  236  ; 

factor  of  safety  of  a,  237 
Brass,  238  ;  annealed,  12  ;  rupture 

of,  87 ;  rod  test  of  a,  109 
Brayshaw  salt  bath  furnace,   261 
Breakdown,  elastic,  13 
Bricks,  testing  of,  206 
Briquettes,  standard,  190 
Brinell's  ball  test,  143 ;  for  cement, 

200 
Brittle  materials  in  torsion,   116  ; 

criterion  of  strength  for,  251 
Brittleness,  9 

Buckton  &  Co.,  Messrs.,  44,  82 
Burr,  Prof.,  166 


C. 


' '  C,"  determination  of ,  2 1 7  ;   values 

of,  133,  216 
Calculation    of    stresses,     Guest's, 

240 
Calibration    of  vertical  machines, 

47 

Calvert  and  Johnson,  Messrs.,  147 
Cambridge  extensometer,  59 
Cambridge    Scientific    Instrument 

Co.,  the,  145 
Carbide,  iron,  11 
Carbon,  8 
Cast  iron,  compression  of,  94;  in 

shear,    157 ;     roller     test,    163 ; 

rules  for,  235  ;   combined  bend- 
ing and  torsion  of,  251 
Cast  steel,  torsion  of,  119 
Castings  for  machinery,  steel,  234 
Cement     testing    machine,     192; 

crushing  machine,    Bailey,  198  ; 

Brinell's  ball  test  for,  200 


Cementite,  11 

Centres  of  higher  education,  4 

Chatellier  cement  test,  192, 
222 

Chemical  analysis  of  steel,  8 

Chrome-vanadium  steel,  heat  treat- 
ment of,  264 

City  and  Guilds  Technical  College, 
257 

Civil  Engineers,  Steel  Committee 
of,  251  ;  Institution  of,  204, 
227 

Clutch,  electric,  42 

Coker,  Prof.,  106,  125,  254  ;  instru- 
ment for  measuring  torsional 
and  bending  strains,  257 

College  laboratories,  experiments 
in,  213 

Combined  stress  test  worked  out, 
249  ;  bending  and  torsion, 
fracture  of  cast  iron  in,  251  ; 
testing  machine,  251  ;  bending 
and  torsion  machine,  Coker's, 
254 

Commercial  test,  full,  5,  85,  217 

Composition,  the  art  of,  6 

Compound  stress,  236  et  seq. 

Compression  shackles,  47  ;  tests, 
89,  219;  specimen,  appearance 
of,  92;  of  cast  iron,  94;  of 
concrete,  194,  222 ;  of  short 
specimens,  219 ;  and  torsion, 
alternate,  220 

Concrete,  determining  conditions 
of  strength  of,  195—199;  tests 
of,  222 

Connecting  rods,  rules  for,  234 

Constants,  useful,  268—273 

Copper,  8,  235,  238 ;  torsion  tests 
of,  129  ;  for  pipes,  235 

Crank-shafts,  rules  for,  234  ;  com- 
bined bending  and  twisting  of, 
236 

Cross-bending  tests,  164 
Crystalline  structure,  9  ;  effects  of 
annealing  on,  10 


INDEX 


279 


D. 


DE  FREMINVILLE,  152 

Deflection  of  beams,  41 

Diagram,     automatic,     80  ;   stress 

strain,  13 
Dillner,  151 
Discipline,  4 
Dixon,  Prof.  Stephpn,  31 
Doubling  tests,  164 
Ductile  materials  in  torsion,  117  ; 

tests  of,  85,  219 
Ductility,  4  ;  of  steel,  11 


E. 


"E,"  values  of,  114 

East  London  College,  161,  254 

Education,  centres  of  higher,  4 

Elastic  breakdown,  13  ;  limit,  86, 
242  ;  range,  102 ;  limit,  deter- 
mination of  by  extensometer, 
218  ;  curve,  obtaining,  220  ; 
limit  and  yield  point,  243 

Elasticity,  modulus  of,  3,  107  ;  of 
materials,  232 

Electric  clutch,  42 

Elongation,  percentage,  7 

Engineering,  31,  181,  236,  241 

Engineering  Standards  Committee, 
84,  189 

Equipment,  4 

Swing's  extensometer,  52,  109 

Examinations,  4 

Extensibility,  13,  14 

Extension,  distribution  of,  87  ;  of 
a  long  wire,  216 

Extensometer,  52,218  ;  Ewing's,  52, 
109 ;  Unwin's,  54  ;  Marten's,  56 ; 
Ashcroft's,  56  ;  Kennedy's,  57  ; 
the  Cambridge,  59  ;  Marten's 
mirror,  63  ;  Morrow's,  63  ;  Stro- 
meyer's  optical,  63  ;  "  rolling 
pin,"  78 


F. 


FACTOR  of  safety,  3  ;  of  a  boiler, 

237 

Failure  by  shear,  93,  95 
Fatigue,   effect    of,    103  ;    testing 

machine,  179 
Ferrite,  11 
Ferro-concrete  beams,  testing   of, 

203 
Flaws     and      surface     markings, 

effects  of,  220 
Fletcher  gas-muffle,  261 
Floor  tests,  ferro- concrete,  204 
Folding  tests,  164 
Forgings  for  machinery,  steel,  234 
Fracture,  appearance   of,   9  ;  of  a 

specimen,    13 ;     of     cement    by 

crushing,     195  ;    testing     small 

specimens    for,    217;  of  various 

materials,  86—89,  217 
Friction,  effect  of  internal,  94,  107 
Furnace,  Brayshaw  salt  bath,  261 


G. 


GAS-MUFFLE,  Fletcher,  261 

Gauge-length,  the,  84 

Genie  Civil,  Le,  200 

Glasgow    and    West    of    Scotland 

Technical  College,  251 
Gold,  7 

Goodman,  Prof.,  183,  251 
Graphite,  12 
Grips,  Wicksteed,  46 
Grosvenor  Square,  floor  tests  at,  205 
Guest,  Mr.  J.  J.,  237;  law,  237  tt 

seq.  ;  tests  on  steel  tubes,  238 
Guillery,  149 
Gun-metal,   torsion  of,  118;  rules 

for,  234 

H. 

HAMMERING  tests,  221,  234 
Hancock,  Prof.,  241—245 


280 


INDEX 


Hand  bending  machine,  Sankey's, 
184 

Hard  steel  rod,  test  of  a,  109 

Hardening,  time  effect  on,  218 ;  of 
Bessemer  steel,  261 

Hardenite,  11 

Hardness  of  steel,  11;  tests,  145; 
factor,  146  ;  numbers,  147  ;  scales 
compared,  154  ;  tests  on  con- 
crete, 222 ;  number  and  tensile 
strength,  relation  between,  222 

Heat  treatment  of  iron,  12 ;  effect 
of,  102  ;  low-temperature,  104 ; 
high- temperature,  104  ;  on 
Bessemer  steel,  260;  of  vana- 
dium-chrome steel,  264 

Ilenning's  stress  strain  recorder,  76 

Homogeneity,  247 

Hooke's  law,  78 

Howard,  188 

Howe,  12 

Hummel,  Prof.,  31,  119 

Hysteresis,  mechanical,  106;  time 
effect  on,  107 


I. 


IMPACT  machine,  Avery,  137 

Impact  tester,  tensile,  138;  testing 
machine,  Seaton  and  Jude's,  143  ; 
testing  machine,  repeat,  143 ;  tests, 
object  of,  137,  220 

India-rubber,  hardness  of,  153 

Institute,  the  Iron  and  Steel,  128, 
152,  245,  260,  264 

Institution  of  Junior  Engineers, 
103  ;  of  Mechanical  Engineers, 
137,  140,  141,  143,  249,  267;  of 
Naval  Architects,  175  ;  of  Civil 
Engineers,  204,  227 

Instruments  of  precision,  handling 
of,  214 

Interference  of  light,  64 

International  Association  for  Test- 
ing Materials,  188 


Iron,  7  ;  carbide,  1 1 
Iron  and  Steel  Institute,  128,  152, 
245,  260,  264 


J. 


JUDE,  Messrs.  Seaton  and,  137 


K. 


KEEP'S  hardness  test,  152  ;  test- 
ing machine,  41 

Kennedy,  Prof.,  78;  testing  ma- 
chine, 23  ;  exteiisometer,  57  ; 
autographic  method,  78 

Kirkaldy,  Sankey  and  Blouiit, 
Messrs.,  40  ;  tests  on  beams,  211 

Knife-edge,  wear  of,  47 


L. 


LABORATORY,  the  testing  of 
materials,  3 

Larard,  Mr.  0.  E,  44 

Laslett,  Mr.  T.,  209 

Lead,  8,  235 

Leatheriness  of  a  material,  185 

Light,  interference  of,  64 

Lilley,  Prof.,  47 

Liverpool,  University  of,  250 

Limit  of  proportionality,  13 ; 
elastic,  13 

Loading,  axial,  46  ;  result  of  non- 
axial,  244 

London,  University  of,  4 

Longitudinal  shear  in  timber, 
208 

Longmuir,  Mr.  P.,  264 

Low  heat  treatment,  effect  of,  104  ; 
effect  of  in  torsion,  126 

M. 

MACHINE  Co.,  Coventry,  the,  162 
Machinery,  steel  castings  for,  234  ; 
forgings  for,  234 


INDEX 


281 


Manchester  School  of  Technology, 

the,  204 
Manganese,  8 

Marking  out  specimens,  214 
Marten,  Prof.,  166  ;  extensometer, 

56  ;  mirror  extensometer,  63 
Martensite,  11 
Mason,  Mr.,  250 
Materials,  structure  of,  8  ;   micro - 

structure  of,  9  ;  of  construction, 

tests    on    the   chief,    227—230 ; 

properties  of,  231 ;  strength  and 

elasticity  of,  232 
Maximum  stress  in  a  tensile  test, 

72  ;  shear  stress,  237 
Me  William,  Prof.  A.,  260 
Mean  diameter,  determination   of, 

91 

Mechanical    properties,    7 ;   treat- 
ment, effect  of,  102  ;  advantage 

of  a  large  testing  machine,  47, 

217 

Metallography,  9 
Micrograph  of  cast  steel,  13 
Microstructure,  9,  221 
Mild  steel  plates  in  tension,  100 ; 

test     of,     110;    in    shear,    157; 

punching  test  on,  160 
Mirror  extensometer,  Marten's,  63 
Modulus     of     elasticity,    3,    107; 

shear,  3  ;    by    bending,  111 ;    of 

rigidity,  132  ;  for  wood,  211 
Morrow's  extensometer,  63 
Mother-of-pearl,  10 
Munich,  25 
Muntz    metal,     ultimate     tension 

tests  on,  86,  113,  131 


N. 


NATIONAL  Physical  Laboratory, 
report,  62  ;  impact  apparatus, 
141;  alternating  stress  machine, 
177 

Naval  brass,  rules  for,  235 


Navier's  theory,  98 

Nickel,  impact  tests  on,  142  ;  steel, 

Hancock's  tests  on,  245 
Non-axial  loading,  results  of,  244, 

247 

Non-ductile  materials,  tests  of,  89 
Northampton  Polytechnic  Institute, 

43 
Notched    specimens,    impact  tests 

on,  220 

Notches,  effect  of,  219 
Note-books,  213 


0. 


"  OMNIBUS  "  testing  machine,  16 
Optical  instruments,    62  ;  extenso- 
meter, Stromeyer's,  63 
Osborne  Eeynolds,  Prof.,  177 
Osciltograph,  stress  strain,  181 
Overstrain,    effect  of  boiling  on, 

104,  219 ;  effect  of,  125,  218 
Owens  College,  177 


P. 


PALLADIUM,  8 

Pearlite,  10 

Percentage  elongation,  7 

Permanent  set,  13 

Perry,  Prof.,  67 

Philosophical  Magazine,  241 

Phosphorus,  8 

Physical  Review,  106 

Physical  Society,  the,  251 

Pig  iron,  grey,  12 

Pinewood,  hardness  of,  153 

Pipes,  copper  for,  235 

Piston  rods,  rules  for,  234 

Plastic  stage,  the,  86 

Platinum,  7 

Poisson's  ratio,  63,  134  ;  values  of, 
135,  216 

Polytechnic  Institute,  Northamp- 
ton, 43 


282 


INDEX 


Popple  well,  Mr.  W.  C.,  204 

Portland  cement,  standard  test  of, 
189 

Potassium  chloride,  262 ;  bichro- 
mate, 262 

Propeller  shafts,  rules  for,  234; 
analysis  of  cuttings  from,  235 

Properties,  mechanical,  8 ;  of 
materials,  231 

Proportionality,  limit  of,  13 

Punching  tester,  159 

Pyrometer,  platinum  resistance,  261 

0. 

QUENCHING  of  Bessemer  steel,  261 

E. 

EATIO     of     maximum     to    mean 

stress,  243 

Eead  and  Macdonald,  Messrs.,  204 
Eecorder,     the     Wicksteed,     79 ; 

autographic,  72 

Eeduction  in  area,  percentage,  7 
Eeinforced  concrete,  tests  of,  202 
Eepeat  impact  testing  machine, 

143  ;  stresses,  183,  221 
Eeport  of  the  test,  5,  215 
Revue  de  Metallurgie,  La,  200 
Eiehle  testing  machine,  36,43,  121 
Eigidity,  modulus  of,  132 
Eing-shaped  specimen,  182 
Eivet  shear,  159 
Eoller  tests,  163 
Eolling-pin  strain  indicator,  57 
Eough  shop  tests,  163 
Eoyal  Society,  Philosophical  Trans- 
actions of,  103, 188 
Eupture,  characteristics  of,  87 

S. 

SAFETY,  factor  of,  3;  of  a  boiler, 

factor  of,  237 
Samples,  preparing,  8 
Sankey,  Messrs.  Blount,  Kirkaldy 

and,  140 


Sankey,  Captain,  168,  264 

Sankey's  hand  bending  machine, 
184 

"  Science  Abstracts,"  264 

Sclerometer,  152 

Scleroscope,  Shore's,  152 

Scoble,  Mr.  Walter,  241,  245,  251  ; 
results  obtained  by,  243 

Scratch  test,  the,  152 

Seaton  and  Jude's  impact  testing 
machine,  143 

Sensitiveness  of  large  testing 
machine,  testing  the,  47,  217 

Set,  permanent,  13 

Setting  test,  222 

Shackles,  design  of,  44 ;  compres- 
sion, 47 

Shafts,  rules  for  crank  and 
propeller,  234 

Shear,  modulus,  3,  135 ;  failure  by, 
93,  95 ;  tests,  double  and  single, 
221  ;  on  the  chief  materials  of 
construction,  tests  in,  227 — 
230  ;  stress,  maximum,  237 

Shearing  tests  on  short  beams, 
221;  tests,  155;  shackles,  155; 
stress,  constancy  of,  240 

Sheffield  University,  12,  177 

Shock,  8 

Silicon,  8 

Silver,  7,  261 

Smith,  Prof.  J.  H.,  178 

Smith,  0.  A.  M.,  182 

Sodium,  light,  64  ;  chloride,  262 

Spangenburg,  181 

Specific  gravity  test,  222 

Specimen,  mild  steel,  80  ;  tension, 
83  ;  making  out  the,  214 

Spherical  seat,  46 

Sphingometer,  the,  65,  247  ;  test- 
ing with  the,  115;  the  torsion, 
124 

Spring,  relation  between  load  and 
extension  of  a,  215;  com- 
pression of  a,  215;  determina- 
tion of  "  0  "  with  a,  217 


INDEX 


283 


Standard  test  pieces,  84 ;  angle  of 
bending,  186 

Standards  Committee,  British 
Engineering,  84 

Stanton,  Dr.,  143,  168,  182  ;  alter- 
nating stress  machine,  177 

Stead,  Mr.  J.  B.,  176 

Steel,  7,  238 ;  physical  properties 
of,  7  ;  hardened,  1 1 ;  tenacity  of, 
11  ;  balls,  tests  of,  161  ;  castings 
for  machinery,  234;  forgings, 
234 ;  tubes,  Guest's  tests  on,  239  ; 
Committee  of  Civil  Engineers, 
251 ;  chrome- vanadium,  264 

Stephen  Dixon,  Prof.,  31 

Stillion,  19 

Stones,  testing  of,  206 

Strain  indicator,  Stromeyer's,  57 

Strength,  ultimate,  13;  of  mate- 
rials, 3,232;  of  concrete,,  deter- 
mining conditions  of,  195 — 199 

Stress,  compound,  236  et  seq. ; 
failure  by  shear,  93,  95 

Stresses,  repeat,  181,  221;  calcula- 
tion of,  Guest's,  240 

Stress  strain  diagram,  13 ;  re- 
corder, Unwin's,  73;  Wick- 
steed's,  75 ;  Henning's,  76 

Stromeyer's  strain  indicator,  57 ; 
optical  extensometer,  63 

Structure  of  materials,  8;  crystal- 
line, 9 

Struts,  tests  of,  47,  219 

Sulphur,  261 

Surface  markings,  effect  of,  220 

Sydney,  University  of,  149,  202 


T. 

TEAK,  hardness  of,  153 

Tempering  of  Bessemer  steel,  262 

Tenacity  of  steel,  11 

Tensile  impact  tester,  138 ;  tests 
of  concrete,  222;  strength  and 
hardness  number,  relation '  be- 
tween, 222 


Tension  specimens,  83 ;  and  com- 
pression, alternate,  220  ;  on  the 
chief  materials  of  construction, 
tests  in,  227—230;  stresses, 
alternating,  170 

Test,  report  of  the,  5  ;  pieces 
standard,  84 ;  of  a  ductile 
material,  85 ;  of  a  non-ductile 
material,  89 ;  compression,  89 

Tests,  the  various,  14 

Testing  machine,  the  "Omnibus," 
16 ;  types  of,  18 ;  vertical,  18 ; 
horizontal,  19  ;  Wicksteed,  21; 
Kennedy,  23 ;  Werder,  24 ;  at 
Birmingham  University,  25 — 31  ; 
Avery,  31;  Amsler,  34;  Biehle, 
36,  43 ;  Bailey  transverse,  39  ; 
Keep's,  41 ;  automatic,  41;  beam, 
64 ;  cement,  192 ;  Bailey  cement, 
193;  experiments  with,  217; 
combined  stress,  251 

Thermo-couple,  Paul,  261 

Thick  cylinder,  to  test  a,  222 

Thuvston  torsion  machine,  121 

Timber,  tension  tests  of,  207,  221 ; 
compression  tests  of,  207 ; 
bending  tests  of,  207 ;  shear 
strength  of,  212;  longitudinal 
shear  in,  208 ;  tests  in  crush- 
ing, 221 ;  beams,  testing  of 
long,  221 

Time  effect,  104,  245,  247;  in 
torsion,  128;  on  wood  beams, 
211  ;  on  hardening,  218 

Tin,  8,  235 

Torsion  machine,  the  Bailey,  119; 
machine,  the  Avery,  121 ;  sphin- 
gometer,  124 ;  experiments  on 
wire,  135 ;  specimens,  fracture 
of,  220  ;  combined  bending  and, 
221 ;  on  the  chief  materials  of 
construction,  tests  in,  227 — 230  ; 
and  bending  strains,  Prof. 
Coker's  instrument  for  measur- 
ing, 257 

Torsion -meter,  238 


284 


INDEX 


Torsional     vibrations,     36,     216; 

stresses,  alternating,  168 
Toughness,  9 
Transactions    of   the   Institute    of 

Naval  Architects,  175 
Tubes,  combined  stress  on,  238 
Turner,  Prof.,  152 
Twist,  angle  of,  117 


U. 

ULTIMATE  strength,  3,  237 
University  of  London,  4  ;   of  Shef- 
field, 12, 177,  260  ;  of  Sydney,  149, 
202;    of  Durham   Philosophical 
Society     Proceedings,     188 ;     of 
Liverpool,  250 
Unwin,  Prof.,  146 
Unwin's    extensometer,  54  ;  stress 
strain     recorder,   73 ;     hardness 
tests,  143 

Upsala,  Benedicks  of,  149 
Useful  constants,  268  tt  seq. 


V. 


VANADIUM-CHROME      steel,     heat 

treatment  of,  264 
Vibrations,  torsional,  36,  216 
Vienna,  25 

W. 

WAHLBERG,  262 
Warren,  Prof.,  149,  202 
Wear  of  knife-edge,  47 


Werder  testing  machine,  24 
Whipple  recorder,  261 
White  metal,  rules  for,  235 
Wicksteed    testing    machine,    21  ; 

grips,  46  ;   stress  strain  recorder, 

75  ;  recorder,  the,  79 
Wire,  torsion  experiments  on,  135, 

216 

Wires,  tests  on,  165,  216 
Wohler,  168,  181 
Wood,  tests  on,  207  ;  shear  strength 

of,  212 
Wooden   beams,   time    effect    on, 

211 

Work  done  in   fracturing  a  speci- 
men, 166 
Wrought  iron,  fracture  of,  9  ;  rod, 

test  of,  111 ;  in  shear,  157 


Y. 


YIELD-POINT,  13;  by  drop  of  the 
beam,  217  ;  stress,  237  ;  raising 
the,  100;  testing  a  small  speci- 
men for,  217;  Scoble's  deter- 
mination of,  242  ;  and  elastic 
limit,  243 ;  determination  of, 
245 

Young's  modulus,  determination 
of,  218;  by  the  extension  of  a 
short  wire,  165,  215 


Z. 


Zmc,  8,  235 
Zurich,  25 


BRADBURY,    AGNEW,    &    CO.  LD.,  PRINTERS,    LONDON   AND    TONBRIDGE. 


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THE    "WESTMINSTER"    SERIES 

Goal.  By  JAMES  TONGE,  M.I.M.E.,  F.G.S.,  etc.  (Lecturer 
on  Mining  at  Victoria  University,  Manchester).  With 
46  Illustrations,  many  of  them  showing  the  Fossils  found 
in  the  Coal  Measures. 

LIST   OF   CONTENTS  :     History.     Occurrence.     Mode   of   Formation 

of  Coal  Seams.     Fossils  of  the  Coal  Measures.     Botany  of  the 

Coal-Measure   Plants.     Coalfields   of  the   British   Isles.     Foreign 

Coalfields.     The  Classification  of  Coals.     The  Valuation  of  Coal. 

Foreign  Coals  and  their  Values.     Uses  of  Coal.     The  Production 

of  Heat  from  Coal.     Waste  of  Coal.     The  Preparation  of  Coal 

for  the  Market.     Coaling  Stations  of  the  World.     Index. 

This  book  on  a  momentous  subject  is  provided    for    the    general 

reader  who  wishes  accurate  knowledge  of  Coal,    its    origin,  position 

and  extent,  and  its  economical  utilization  and  application. 

Iron  and  Steel.    By  J.  H.  STANSBIE,  B.Sc.  (Lond.),  F.I.C. 

With  86  Illustrations. 

LIST  OF  CONTENTS:  Introductory.  Iron  Ores.  Combustible  and 
other  materials  used  in  Iron  and  Steel  Manufacture.  Primitive 
Methods  of  Iron  and  Steel  Production.  Pig  Iron  and  its  Manu- 
facture. The  Refining  of  Pig  Iron  in  Small  Charges.  Crucible 
and  WTeld  Steel.  The  Bessemer  Process.  The  Open  Hearth 
Process.  Mechanical  Treatment  of  Iron  and  Steel.  Physical 
and  Mechanical  Properties  of  Iron  and  Steel.  Iron  and  Steel 
under  the  Microscope.  Heat  Treatment  of  Iron  and  Steel.  Elec- 
tric Smelting.  Special  Steels.  Index. 

The  aim  of  this  book  is  to  give  a  comprehensive  view  of  the  modern 
aspects  of  iron  and  steel,  together  with  a  sufficient  account  of  its  his- 
tory to  enable  the  reader  to  follow  its  march  of  progress.  The  methods 
of  producing  varieties  of  the  metal  suitable  to  the  requirements  of 
the  engineer,  foundryman  and  mechanician  are  described  so  that  the 
worker  may  learn  the  history  of  the  material  he  is  handling. 

Natural  Sources  of  Power.    By  ROBERT  S.  BALL,  B.Sc., 

A.M.Inst.C.E.  With  104  Diagrams  and  Illustrations. 
CONTENTS  :  Preface.  Units  with  Metric  Equivalents  and  Abbre- 
viations. Length  and  Distance.  Surface  and  Area.  Volumes. 
Weights  or  Measures.  Pressures.  Linear  Velocities,  Angular 
Velocities.  Acceleration.  Energy.  Power.  Introductory 
Water  Power  and  Methods  of  Measuring.  Application  of  Water 
Power  to  the  Propulsion  of  Machinery.  The  Hydraulic  Turbine. 
Various  Types  of  Turbine.  Construction  of  Water  Power  Plants. 
Water  Power  Installations.  The  Regulation  of  Turbines.  Wind 
Pressure,  Velocity,  and  Methods  of  Measuring.  The  Application 
of  Wind  Power  to  Industry.  The  Modern  Windmill.  Con- 
structional Details.  Power  of  Modern  Windmills.  Appendices 
A,B,C  Index. 
Two  departments  of  Engineering  and  their  applications  to  industry 

form  the  subject  of  this  volume  :    the  "  natural  "  sources  of  water 

(   2    ) 


THE    "WESTMINSTER"    SERIES 

and  wind  power  which  supply  mechanical  energy  without  any  inter- 
mediate stage  of  transformation.  Most  people  will  be  surprised  at 
the  extent  to  which  these  natural  power  producers  are  used.  The 
widespread  application  of  water  power  is  generally  known,  but  it  is 
interesting  to  learn  that  the  demand  for  windmills  was  never  so  great 
as  it  is  to-day,  and  there  are  signs  of  abnormal  expansion  in  the  direc- 
tion of  their  useful  application  in  the  great  agricultural  countries  of 
the  world.  Though  primarily  of  importance  to  the  engineer,  this  work 
will  be  of  great  interest  to  every  manufacturer  who  in  economizing 
his  means  of  power  production  can  take  the  natural  forces  that  lie 
to  his  hand  and  harness  them  in  his  service.  The  author  is  the  son 
of  Sir  Robert  Ball,  the  eminent  mathematician  and  astronomer. 

Liquid  and  Gaseous  Fuels,  and  the  Part  they  play 
in  Modern  Power  Production.  By  Professor 
VIVIAN  B.  LEWES,  F.I.C.,  F.C.S.,  Prof,  of  Chemistry, 
Royal  Naval  College,  Greenwich.  With  54  Illustrations. 

LIST  OF  CONTENTS  :  Lavoisier's  Discovery  of  the  Nature  of  Com- 
bustion, etc.  The  Cycle  of  Animal  and  Vegetable  Life.  Method 
of  determining  Calorific  Value.  The  Discovery  of  Petroleum 
in  America.  Oil  Lamps,  etc.  The  History  of  Coal  Gas.  Calorific 
Value  of  Coal  Gas  and  its  Constituents.  The  History  of  Water 
Gas.  Incomplete  Combustion.  Comparison  of  the  Thermal 
Values  of  our  Fuels,  etc.  Appendix.  Bibliography.  Index. 

The  subject  of  this  book  has,  during  the  last  decade,  assumed  such 
importance  that  it  is  hoped  this  account  of  the  history  and  develop- 
ment of  the  use  of  various  forms  of  combustible  liquids  and  gases 
for  the  generation  of  energy  may  do  some  service  in  its  advancement. 

Electric  Power  and  Traction*  By  F.  H.  DAVIES, 
A.M.I.E.E.  With  66  Illustrations. 

LIST  OF  CONTENTS  :  Introduction.  The  Generation  and  Distri- 
bution of  Power.  The  Electric  Motor.  The  Application  of 
Electric  Power.  Electric  Power  in  Collieries.  Electric  Power 
in  Engineering  Workshops.  Electric  Power  in  Textile  Factories. 
Electric  Power  in  the  Printing  Trade.  Electric  Power  at  Sea. 
Electric  Power  on  Canals.  Electric  Traction.  The  Overhead 
System  and  Track  Work.  The  Conduit  System.  The  Surface 
Contact  System.  Car  Building  and  Equipment.  Electric  Rail- 
ways. Glossary.  Index. 

The  majority  of  the  allied  trades  that  cluster  round  the  business  of 
electrical  engineering  are  connected  in  some  way  or  other  with  its  power 
and  traction  branches.  To  members  of  such  trades  and  callings,  to 
whom  some  knowledge  of  applied  electrical  engineering  is  desirable 
if  not  strictly  essential,  the  book  is  particularly  intended  to  appeal. 
It  deals  almost  entirely  with  practical  matters,  and  enters  to  some 
extent  into  those  commercial  considerations  which  in  the  long  run 
must  overrule  all  others. 

(3  ) 


THE    "WESTMINSTER"    SERIES 

Town  Gas  and  its  Uses  for  the  Production  of 
Light,  Heat,  and  Motive  Power,  By  W.  H.  Y. 
WEBBER,  C.E.  With  71  Illustrations. 

LIST  OF  CONTENTS  :  The  Nature  and  Properties  of  Town  Gas.  The 
History  and  Manufacture  of  Town  Gas.  The  Bye-Products  of 
Coal  Gas  Manufacture.  Gas  Lights  and  Lighting.  Practical 
Gas  Lighting.  The  Cost  of  Gas  Lighting.  Heating  and  Warm- 
ing by  Gas.  Cooking  by  Gas.  The  Healthfulness  and  Safety 
•  of  Gas  in  all  its  uses.  Town  Gas  for  Power  Generation,  including 
Private  Electricity  Supply.  The  Legal  Relations  of  Gas  Sup- 
pliers, Consumers,  and  the  Public.  Index. 

The  "  country,"  as  opposed  to  the  "  town,"  has  been  denned ''as 
"  the  parts  beyond  the  gas  lamps."  This  book  provides  accurate 
knowledge  regarding  the  manufacture  and  supply  of  town  gas  and  its 
uses  for  domestic  and  industrial  purposes.  Few  people  realize  the 
extent  to  which  this  great  industry  can  be  utilized.  The  author  has 
produced  a  volume  which  will  instruct  and  interest  the  generally  well 
informed  but  not  technically  instructed  reader. 

Electro-Metallurgy*  By  J.  B.  C.  KERSHAW,  F.I.C.  With 
61  Illustrations. 

CONTENTS  :  Introduction  and  Historical  Survey.  Aluminium. 
Production.  Details  of  Processes  and  Works.  Costs.  Utiliza- 
tion. Future  of  the  Metal.  Bullion  and  Gold.  Silver  Refining 
Process.  Gold  Refining  Processes.  Gold  Extraction  Processes. 
Calcium  Carbide  and  Acetylene  Gas.  The  Carbide  Furnace  and 
Process.  Production.  Utilization.  Carborundum.  Details  of 
Manufacture.  Properties  and  Uses.  Copper.  Copper  Refin- 
ing. Descriptions  of  Refineries.  Costs.  Properties  and  Utiliza- 
tion. The  Elmore  and  similar  Processes.  Electrolytic  Extrac- 
tion Processes.  Electro-Metallurgical  Concentration  Processes. 
Ferro-alloys.  Descriptions  of  Works.  Utilization.  Glass  and 
Quartz  Glass.  Graphite.  Details  of  Process.  Utilization.  Iron 
and  Steel.  Descriptions  of  Furnaces  and  Processes.  Yields  and 
Costs.  Comparative  Costs.  Lead.  The  Salom  Process.  The  Betts 
Refining  Process.  The  Betts  Reduction  Process.  White  Lead  Pro- 
cesses. Miscellaneous  Products.  Calcium.  Carbon  Bisulphide. 
Carbon  Tetra-Chloride.  Diamantine.  Magnesium.  Phosphorus. 
Silicon  and  its  Compounds.  Nickel.  Wet  Processes.  Dry 
Processes.  Sodium.  Descriptions  of  Cells  and  Processes.  Tin. 
Alkaline  Processes  for  Tin  Stripping.  Acid  Processes  for  Tin 
i  Stripping.  Salt  Processes  for  Tin  Stripping.  Zinc.  Wet  Pro- 
cesses. Dry  Processes.  Electro-Thermal  Processes.  Electro- 
Galvanizing.  Glossary.  Name  Index. 

The  subject  of  this  volume,  the  branch  of  metallurgy  which  deals 
with  the  extraction  and  refining  of  metals  by  aid  of  electricity,  is 
becoming  of  great  importance.  The  author  gives  a  brief  and  clear 
account  of  the  industrial  developments  of  electro-metallurgy,  in  lan- 
guage that  can  be  understood  by  those  whose  acquaintance  with  either 

(  4  ) 


THE     '  WESTMINSTER '     SERIES 

chemical  or  electrical  science  may  be  but  slight.  It  is  a  thoroughly 
practical  work  descriptive  of  apparatus  and  processes,  and  commends 
itself  to  all  practical  men  engaged  in  metallurgical  operations,  as  well 
as  to  business  men,  financiers,  and  investors. 

Radio-Telegraphy*  By  C.  C.  F.  MONCKTON,  M.I.E.E. 
With  173  Diagrams  and  Illustrations. 

CONTENTS  :  Preface.  Electric  Phenomena.  Electric  Vibrations. 
Electro-Magnetic  Waves.  Modified  Hertz  Waves  used  in  Radio - 
Telegraphy.  Apparatus  used  for  Charging  the  Oscillator.  The 
Electric  Oscillator  :  Methods  of  Arrangement,  Practical  Details. 
The  Receiver  :  Methods  of  Arrangement,  The  Detecting  Ap- 
paratus, and  other  details.  Measurements  in  Radio-Telegraphy. 
The  Experimental  Station  at  Elmers  End  :  Lodge-Muirhead 
System.  Radio  -  Telegraph  Station  at  Nauen  :  Telefunken 
System.  Station  at  Lyngby :  Poulsen  System.  The  Lodge- 
Muirhead  System,  the  Marconi  System,  Telefunken  System,  and 
Poulsen  System.  Portable  Stations.  Radio-Telephony.  Ap- 
pendices :  The  Morse  Alphabet.  Electrical  Units  used  in  this 
Book.  International  Control  of  Radio-Telegraphy.  Index. 

The  startling  discovery  twelve  years  ago  of  what  is  popularly  known 
as  Wireless  Telegraphy  has  received  many  no  less  startling  additions 
since  then.  The  official  name  now  given  to  this  branch  of  electrical 
practice  is  Radio-Telegraphy.  The  subject  has  now  reached  a  thor- 
oughly practicable  stage,  and  this  book  presents  it  in  clear,  concise 
form.  The  various  services  for  which  Radio-Telegraphy  is  or  may 
be  used  are  indicated  by  the  author.  Every  stage  of  the  subject  is 
illustrated  by  diagrams  or  photographs  of  apparatus,  so  that,  while 
an  elementary  knowledge  of  electricity  is  presupposed,  the  bearings 
of  the  subject  can  be  grasped  by  every  reader.  No  subject  is  fraught 
with  so  many  possibilities  of  development  for  the  future  relationships 
of  the  peoples  of  the  world. 

India-Rubber  and  its  Manufacture,  with  Chapters 
on  Gutta-Percha  and  Balata.  By  H.  L.  TERRY, 
F.I.C.,  Assoc.Inst.M.M.  With  Illustrations. 

LIST  OF  CONTENTS  :  Preface.  Introduction  :  Historical  and 
General.  Raw  Rubber.  Botanical  Origin.  Tapping  the  Trees. 
Coagulation.  Principal  Raw  Rubbers  of  Commerce.  Pseudo- 
Rubbers.  Congo  Rubber.  General  Considerations.  Chemical 
and  Physical  Properties.  Vulcanization.  India-rubber  Planta- 
tions. India-rubber  Substitutes.  Reclaimed  Rubber.  Washing 
and  Drying  of  Raw  Rubber.  Compounding  of  Rubber.  Rubber 
Solvents  and  their  Recovery.  Rubber  Solution.  Fine  Cut  Sheet 
and  Articles  made  therefrom.  Elastic  Thread.  Mechanical 
Rubber  Goods.  Sundry  Rubber  Articles.  India-rubber  Proofed 
Textures.  Tyres.  India-rubber  Boots  and  Shoes.  Rubber  for 
Insulated  Wires.  Vulcanite  Contracts  for  India-rubber  Goods. 

(  5  ) 


THE     'WESTMINSTER"    SERIES 

The  Testing  of  Rubber  Goods.     Gutta-Percha.     Balata.     Biblio- 
graphy.    Index. 

Tells  all  about  a  material  which  has  grown  immensely  in  com- 
mercial importance  in  recent  years.  It  has  been  expressly  written 
for  the  general  reader  and  for  the  technologist  in  other  branches  of 
industry. 

Glass  Manufacture.  By  WALTER  ROSENHAIN,  Superin- 
tendent of  the  Department  of  Metallurgy  in  the  National 
Physical  Laboratory,  late  Scientific  Adviser  in  the  Glass 
Works  of  Messrs.  Chance  Bros,  and  Co.  With  Illustra- 
tions. 

CONTENTS  :  Preface.  Definitions.  Physical  and  Chemical  Qualities. 
Mechanical,  Thermal,  and  Electrical  Properties.  Transparency 
and  Colour.  Raw  materials  of  manufacture.  Crucibles  and 
Furnaces  for  Fusion.  Process  of  Fusion.  Processes  used  in 
Working  of  Glass.  Bottle.  Blown  and  Pressed.  Rolled  or 
Plate.  Sheet  and  Crown.  Coloured.  Optical  Glass :  Nature 
and  Properties,  Manufacture.  Miscellaneous  Products.  Ap- 
pendix. Bibliography  of  Glass  Manufacture.  Index. 

This  volume  is  for  users  of  glass,  and  makes  no  claim  to  be  an  ade- 
quate guide  or  help  to  those  engaged  in  glass  manufacture  itself.  For 
this  reason  the  account  of  manufacturing  processes  has  been  kept 
as  non-technical  as  possible.  In  describing  each  process  the  object 
in  view  has  been  to  give  an  insight  into  the  rationale  of  each  step,  so 
far  as  it  is  known  or  understood,  from  the  point  of  view  of  principles 
and  methods  rather  than  as  mere  rule  of  thumb  description  of  manu- 
facturing manipulations.  The  processes  described  are,  with  the 
exception  of  those  described  as  obsolete,  to  the  author's  definite  know 
ledge,  in  commercial  use  at  the  present  time. 

Precious  Stones.  By  W.  GOODCHILD,  M.B.,  B.Ch.  With 
42  Illustrations.  With  a  Chapter  on  Artificial 
Stones.  By  ROBERT  DYKES. 

LIST  OF  CONTENTS  :  Introductory  and  Historical.  Genesis  of 
Precious  Stones.  Physical  Properties.  The  Cutting  and  Polish- 
ing of  Gems.  Imitation  Gems  and  the  Artificial  Production  of 
Precious  Stones.  The  Diamond.  Fluor  Spar  and  the  Forms  of 
Silica.  Corundum,  including  Ruby  and  Sapphire.  Spinel  and 
Chrysoberyl.  The  Carbonates  and  the  Felspars.  The  Pyroxene 
and  Amphibole  Groups.  Beryl,  Cordierite,  Lapis  Lazuli  and  the 
Garnets.  Olivine,  Topaz,  Tourmaline  and  other  Silicates.  Phos- 
phates, Sulphates,  and  Carbon  Compounds. 

An  admirable  guide  to  a  fascinating  subject. 

(  6  ) 


THE     '  WESTMINSTER  "    SERIES 

Patents,  Designs  and  Trade  Marks  :  The  Law 
and  Commercial  Usage*  By  KENNETH  R.  SWAN, 
B.A.  (Oxon.),  of  the  Inner  Temple,  Barrister-at-Law. 

CONTENTS  :  Table  of  Cases  Cited — Part  I. — Letters  Patent.  Intro- 
duction. General.  Historical.  I.,  II.,  III.  Invention,  Novelty, 
Subject  Matter,  and  Utility  the  Essentials  of  Patentable  Invention. 
IV.  Specification.  V.  Construction  of  Specification.  VI.  Who 
May  Apply  for  a  Patent.  VII.  Application  and  Grant.  VIII. 
Opposition.  IX.  Patent  Rights.  Legal  Value.  Commercial 
Value.  X.  Amendment.  XI.  Infringement  of  Patent.  XII. 
Action  for  Infringement.  XIII.  Action  to  Restrain  Threats. 
XIV.  Negotiation  of  Patents  by  Sale  and  Licence.  XV.  Limita- 
tions on  Patent  Right.  XVI.  Revocation.  XVII.  Prolonga- 
tion. XVIII.  Miscellaneous.  XIX.  Foreign  Patents.  XX. 
Foreign  Patent  Laws  :  United  States  of  America.  Germany. 
France.  Table  of  Cost,  etc.,  of  Foreign  Patents.  APPENDIX  A. — 
i.  Table  of  Forms  and  Fees.  2.  Cost  of  Obtaining  a  British 
Patent.  3.  Convention  Countries.  Part  II. — Copyright  in 
Design.  Introduction.  I.  Registrable  Designs.  II.  Registra- 
tion. III.  Marking.  IV.  Infringement.  APPENDIX  B. — i. 
Table  of  Forms  and  Fees.  2.  Classification  of  Goods.  Part 
III. — Trade  Marks.  Introduction.  I.  Meaning  of  Trade  Mark. 
II.  Qualification  for  Registration.  III.  Restrictions  on  Regis- 
tration. IV.  Registration.  V.  Effect  of  Registration.  VI. 
Miscellaneous.  APPENDIX  C. — Table  of  Forms  and  Fees.  INDICES. 
i.  Patents.  2.  Designs.  3.  Trade  Marks. 

This  is  the  first  book  on  the  subject  since  the  New  Patents  Act. 
Its  aim  is  not  only  to  present  the  existing  law  accurately  and  as  fully 
as  possible,  but  also  to  cast  it  in  a  form  readily  comprehensible  to  the 
layman  unfamiliar  with  legal  phraseology.  It  will  be  of  value  to  those 
engaged  in  trades  and  industries  where  a  knowledge  of  the  patenting 
of  inventions  and  the  registration  of  trade  marks  is  important.  Full 
information  is  given  regarding  patents  in  foreign  countries. 

The  Book;  Its  History  and  Development*  By 
CYRIL  DAVENPORT,  V.D.,  F.S.A.  With  7  Plates  and 
126  Figures  in  the  text. 

LIST  OF  CONTENTS  :  Early  Records.  Rolls,  Books  and  Book 
bindings.  Paper.  Printing.  Illustrations.  Miscellanea. 
Leathers.  The  Ornamentation  of  Leather  Bookbindings  without 
Gold.  The  Ornamentation  of  Leather  Bookbindings  with  Gold. 
Bibliography.  Index. 

The  romance  of  the  Book  and  its  development  from  the  rude  inscrip- 
tions on  stone  to  the  magnificent  de  Luxe  tomes  of  to-day  have 
never  been  so  excellently  discoursed  upon  as  in  this  volume.  The 
history  of  the  Book  is  the  history  of  the  preservation  of  human  thought. 
This  work  should  be  in  the  possession  of  every  book  lover. 

(7) 


Van  NostrandV  Westminster"  Series 


LIST    OF    NEW  AND    FORTHCOMING 
VOLUMES. 

The  Gas   Engine.     By  Captain  RYALL  SANKEY, 

M.I.M.E 

Timber.     By  J.  R.  BATERDEN,  A.M.I.C.E. 
Steam  Engines.     ByJ.  T.   ROSSITER,   M.I.E.E., 

A.M.I.M.E. 
Electric  Lamps.     By  MAURICE  SOLOMON,  A.C.G.L, 

A.M.LE.E. 

The  Railway  Locomotive.    By  VAUGHAN  PENDRED, 

M.I.Mech.E. 

Pumps  and  Pumping  Machinery.     By  JAMES  W. 

ROSSITER,  A.M.I.M.E. 

Workshop  Practice.  By  Professor  G.  F.  CHAR- 
NOCK,  A.M.I.C.E.,  M.I.M.E. 

Textiles  and  their  Manufacture.  By  ALDRED  BAR- 
KER, M.Sc. 

The   Precious  Metals.       By  THOMAS   K.    ROSE, 

D.Sc.,  of  the  Royal  Mint. 

Photography.  By  ALFRED  WATKINS,  Past  Presi- 
dent of  the  Photographic  Convention. 

Commercial  Paints  and  Painting.  By  A.  S.  JEN- 
NINGS, Hon.  Consulting  Examiner,  City  and  Guilds  of 
London  Institute. 

Decorative  Glass  Processes.    By  A.  L.  DUTHIE. 
Brewing  and  Distilling.     By  JAMES  GRANT,  F.C.S. 
Wood  Pulp  and  Its  Applications.     By  C.  F.  CROSS, 

E.  J.  BE  VAN  and  R.  W.  SINDALL. 

The  Manufacture  of  Paper.     By  R.  W.  SINDALL. 
Wood  Working  Machinery.    By  STAFFORD  RAN- 

SOME. 


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